Why is there no option for for an affordable engine for experimental/home built aircraft?

In the 50-100 horse power range the builder has a few options. Some manufacturers such as Rotax and Hirth offer somewhat moderately priced engines and there are several reasonably priced VW conversions. For those needing engines in the 150-200 hp range, however, there are few choices outside of the two major manufacturers. And there is NOTHING reasonable about those. For example, a recent ad in Trade a Plane listed the price of a new 150 hp Lycoming O-320 at well over $40,000.00! The prices just go up from there. What about a reconditioned or overhauled unit? Well, those started at over $25,000.00 in the same magazine. Some people will say that the high price is because they are Certified engines and the certification process is expensive and time consuming. We are talking here about an engine that was first put in service in 1953 and was developed from an engine designed in the 1930's! One would think that Lycoming would have had ample time to recoup their development and certification costs in the ensuing 63 years. Oh yes, there have been many improvements over the years. In 1961 the IO-320, a fuel injected version, was introduced. Other changes included different magnetos (the fact that we are still using magnetos says a lot), different engine mounts, different prop hubs and, well, that is pretty much it. Things are much the same at Continental.
In contrast, a quick look at some automotive racing supply websites, such as Summit, will show that a brand new 430 hp aluminum block Chevy LS3 engine costs $5931.97. Less than $6K for a modern fuel injected engine built with modern materials and first placed in service this century (2008)! But Chevy turns out a ton of these motors for each one Lycoming makes and the market is so much smaller in aviation! True, but the LS3