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There are some software add-ons and processes to change the URLs, but if all you got paid for is a little work on flat pages you're in for a lot more and it's really up to the developer to implement those.
I've been in the situation - twice, actually - and the developers wouldn't do a thing to change it. Plus, all the dynamic pages within categories had the same, identical titles, headers and all.
>>just a few hours work with META, H1, H2.
Those won't do it, the easiest way other than a fix for the dymamic pages is to create html content pages and just link into the shopping cart from there.