It all depends how you want to build it. A race type bike or a trail type bike.
Use your search function on here as well as the web. You dont see a lot of High Performance modified (motors) 185/200's. I know they should be out there. Even when the 200x hit the market there were still a lot of 185/200's hitting the track. I have a friend with a super highly modified 200 motor. Stroker crank, ported head, double roller cam, etc. It can be bought if the price is right.
JWheeler would be a good start for custom aftermarket goodies for the 185.
* 1978 ATC 90/180 Pauter PJ1 / Springer "Team BAPP" Bike *
* 1980 ATC 110/180 "Danny's Machine Works" 3D Sprint Dune Bike *
* Nicholson 500 Race Bike *
* HPATC Yamaha RD350 "Big Moe" Trike *