There is really no easy way to answer a financial question. You need to start by figuring out how many points you may wish to own. Nightly costs vary widely depending upon what resort(s) you hope to stay at, room size, view, how many nights per trip and how many trips per year. Some people get by with 100-150 points while others own hundreds to meet their needs.
Then you need to consider which Home resort is the best fit. At your Home resort (the location you actually own), you can book up to 11 months in advance of arrival. At other resorts you can only book 7 months prior to arrival. In many circumstances, that Home resort priority be the difference between getting a room and not getting a room. The Beach Club Villas are difficult to book at 7 months pretty much year-round. Other hard to book locations/categories include BoardWalk Standard View and BoardWalk View, Animal Kingdom Villas concierge, Bay Lake Tower Magic Kingdom View and Standard View, etc. The Grand Californian at Disneyland only has 50 villas total so that one will always be a crapshoot.
Home resort also determines how long you will own the DVC points. All DVC ownership has a fixed ending date and it varies by resort. If you buy into the BoardWalk or Beach Club, you will own the points for only about 30 years--those deeds return to Disney on 1/31/2042. At the other end of the spectrum, the Aulani resort in Hawaii runs into 2062 giving you 50+ years of ownership.
Points can be purchased direct from DVC or via a resale vendor. Buying resale tends to be more complicated and time consuming but can yield significant savings. In many ways, it's like buying a house from the builder vs. the current owners. When you buy from the builder, the price is typically non-negotiable and the process is relatively smooth. Buying from a current owner often involves negotiation and waiting on the other party to sign contracts, etc.
When you buy direct from DVC, you can often make your first reservation the very same day. Prices are non-negotiable. They will pro-rate your annual dues for the first year and typically give you what amounts to the prior year's points. Financing is easy. All of the official documents are shipped to your house for a signature; sign at your leisure and return in the pre-paid envelope. You can purchase the exact number of points and Use Year that you desire.
But Disney's prices are over $100 per point in most cases.
Buying resale you are dealing with an owner looking to sell his/her contract. First you need to find a contract with the number of points, Home resort and Use Year that you are seeking. Owners cannot sub-divide their contracts so if you want 180 points at Saratoga Springs with a February Use Year, you have to wait for that exact contract to appear on the resale market.
You'll have to come to an agreement on price and other terms. You will have to weigh the available points balance of the contract. It's not uncommon for sellers to have used some or all of the current year's points before selling their contract. Some will even "borrow" points from next year before selling. You could find the perfect resale listing...only to discover that the current owner has used all of the points for 2011 and 2012. If you buy, you won't have any points to use until the 2013 Use Year.
Best case scenario for making the first reservation in a resale is about 60 days from the time you make the offer. The buyer and seller need to sign and return contracts. Then the offer is submitted to Disney for review. Disney has Right of First Refusal on all resale offers--meaning that they could opt to buy the contract at YOUR terms if they so desire. Disney hasn't been particularly aggressive in buying back contracts these days, but they do still get up to 30 days to review the offer.
Even if Disney waives ROFR, the formal closing must still occur and then the contract is sent on to DVC so they can recognize you as the new owner. Overall, it's a 60+ day process before you will be acknowledged as the new owner and able to make a reservation. And throughout that process, many things could happen to derail the purchase. None of these things would put your funds at risk, but you could end up having to give up on a contract and start over from scratch.
Also note that resale points can no longer be used for many non-DVC options. Resale points cannot be used for anything in what Disney calls the Disney Collection, Concierge Collection or Adventurer Collection. Included in those restrictions are Disney Cruise Line, Adventures by Disney and all non-DVC resorts worldwide (Disneyland Hotel, Grand Floridian, resorts at Disneyland Paris, etc.)
Don't mean to scare you off of the resale process. Many have seamless buying experiences, are comfortable with the restrictions and save thousands of dollars. But others get frustrated with the delays, choose to work with sellers or resale agents who don't know what they are doing, don't want to be prohibited from using points for a Disney Cruise or other non-DVC destination. That's the choice you need to make.
In terms of price, you can find some recent numbers here:
http://dvcnews.com/index.php/dvc-program/financial/pricing-a-promotions
You're looking at $100+ per point for the likes of Bay Lake Tower or Aulani. Even at those prices, I think buying BLT or Aulani direct from Disney is reasonable given the full 50 years of ownership.
Click on the Timeshare Store link above for a look at resale asking prices. You can probably get some resorts in the $50-60 neighborhood but make sure you factor in the shorter ownership period, value of Home resort booking advantage and the resale purchase restrictions.
Good luck.
