IMO the extension doesn't matter for search engines, and costly ??? Is free, with apache mod rewrite (a few lines on your .htaccess server file) you can user wherever URL you want, for: static pages, perl pages, asp pages ...
It doesn't matter which you use, what does matter is that the coding is as clean and error free as possible and that the site has good rich content, mixed in with your relevant keywords of course, to get the good Goog positions!!
as long as it's codes are clean and bots friendly (eliminate unnecessary codes, use css) it will be good on SE's simple sites use html while commercial sites with special features use different language such asp, php
It dose not matter what ever the page extension is, just make sure the exported html is optimized, go with text browser to confirm you pages content the same way the search engines will see it.