So, I guess from your client's perspective, your $15.00 hammer could prove more expensive in the long run if you become subsequently unavailable to maintain their application in the future and they have to start all over again with another new system redeveloped using a different technology.

Lets not forget that really clever stuff today gets included with the tool in 3 years. Example- LINQ. By your own logic, once LINQ enters the mainstream, all that complex pre-LINQ dotNET data-munging stuff is at risk. The $25 hammer may become a $50 hammer. ;-) And the vendor who delivers a $15 hammer today then leap-frogs straight to LINQ tomorrow may have huge business advantage.

IMHO it comes down to a viable upgrade path. Example- Quickbooks. Quickbooks became the Western World's most popular accounting tool using completely unfashionable technology, including local data stores long after "everybody knew" that was a bad idea. Then last year Intuit delivered an upgrade that converted the proprietary data to a pseudo-C/S-backend. Many customers hated the upgrade. I doubt Quickbooks would have been as popular if it inflicted pain every time a development tool developed new abilities that rendered existing code obsolete. IMHO the inherent stability and lack of wild change in VFP has been one of its strengths, just as it has been one of Quickbooks's strengths.

Obviously if your customers insist on dotNET, that's what you have to do. But the Quickbooks experience does tend to suggest that millions of businesses do not fall into that category. Those sorts of businesses are likely to appreciate a $10 saving on a hammer purchased today as well. ;-)