I think you are underestimating the cost of live trees. I doubt you could get a single live tree moved into Mainstreet for $5,000. A 50 foot tree is probably going to set you back almost 50,000 not including the cost of labor in removing the existing tree and planting the new one. Large trees aren't cheap and even worse is the ability to plant one so that it survives, the roots below the ground will generally extend 2 or 3 times the diameter of the drip line so you would be needing to tear up a substantial amoung of the mainstreet area just to deal with the roots. I really don't think it is feasible to plant a big tree there.