I can put a little more detail to help you @asjdsm ...
1 - upto 110cc non racing engines are readily available in market already and price is from 20k to 28K depending upon quality and accessories with it (carb/cdi/rectifier e.t.c...)
2 - For 125cc non racing engine you will have to import.
3 - For 125,140,150,160,180cc sports type variants which fit bolt on to Chondas the price can be higher then what you mentioned.
All the above mentioned engines not only have bigger pistons, but also have bigger crank, weight, Reduction ration, Clutch, gear ratio, and for racing variants most of them are Liquid (Oil) Cold with higher compression ratios
Some Pictures or non racing 110~125, Oil Coled, water cooled, 150~140~180~200, and 4 valve racing engines which can be sourced.
(I think you should add these to main post):