no its not a bolt on fittable needs to replace engine mounts.
I have 250cc engines available in OHV setup.
There rated output its 16HP and 17.5Nm/ft and Max output is 18Hp and 22Nm/ft a bike like RP or a GS150 can do a power wheelie, do Slow, stand on Burnouts, and Cruise on above 1oo or 110kmh for hours "litterly" on high ways with Fuel average of some where around 35~40km/Liter.
In 200cc category horse power is around in same figures but toure is less so you cant do a power wheelie but a clutch wheele, and it can cruise on same top end ...
both variants can be arranged.
If you are looking for a 250cc Twin Cylinder engine then that is expensive, around 80k for orignal rebel engine, night hawk engine might be found in around 50k, its Chinese replica can be found some where arounf 10k to 30k depending on condition and qaulity of copy.