The problem with piston singles since about 1975 is they are not scrapped out in high enough numbers to be replaced by modernized units like cars and trucks are. That Skycatcher sold in 2010 will still be tied down somewhere in the local airport world in 2050, perhaps with an owner hauling mogas through the fence at midnight to fuel it. There is no conspiracy, just insufficient numbers to flush the system of older airplanes.
A lot of the price of leaded avgas is in the heavy taxes, the tiny scale of production, and the fact it is not traded as a commodity. The cost of the lead content is a fairly minor factor. Switching the GA fleet over to no-lead engines will not change the price of avgas very much if at all. The only way to get a serious drop in the price of avgas is to do away with avgas altogether and go to mogas. That is not going to happen, but more power to those who have the biceps to haul it from the mini-mart.
The main motivation for biofuels is having something ready when the EPA finally says "no more lead", and when as Rick points out there is another huge dip in the production of oil. Cheap avgas isn't the only goal although it would be nice.
We presently have a bonus depreciation tax break to spur new airplane sales. See
AOPA Bonus Depreciation article 1 and
AOPA Bonus Depreciation article 2. The problem with this is it only applies to business aircraft and I think, aircraft costing over $200k; it does nothing to sell sport planes or remove any lead burners from the market. There needs to be a cash for clunkers offer extended to outdated piston airplanes added to the existing tax depreciation incentive. This would help get rid of the lead burners, stimulate sales of new aircraft, and stimulate R&D in one move. Bring in your Lyco 360 and go out with the no-lead version, or get a relatively inexpensive brand-new airplane.