Brake kit from other cars, if modded properly will work.
One problem with modding is that the disc isn't centered properly, so you get vibration at higher speeds, if done properly, should be no problem. Another is clearance with rims. Certain rims cannot fit monoblock/twinblock caliper due to spoke design.
Brake function isn't 100% caliper only. Brake pad compound is also a factor. I tried before cheap pads, brake worked quite okay, but wasn't as good as expensive ones. It also ate my rotor, so in the end, it wasn't as cheap as it appeared at first.