What engines are you considering?
The Zongshen 250 (249cc) that came with my Templar X is available on eBay for about 500 bucks (maybe $70 shipping). But for about 100 more, the liquid cooled Zongshen 300 (279cc) 4valve can be had via Alibaba. Shipping unknown ($300 maybe?). I think that 300 will fit in my frame OK. Probably have to remove the tank for valve adjust. But I have mounting points for oil cooler, or radiators. My engine is new, so hard to justify at the moment lol !!
But still tempting