External femur is ridiculously dangerous and complication prone (femur muscles are stronger and exert more pressure on the frame). I'm not a doctor though so take what I say with a grain of salt. If you can't afford internal, I would strongly suggest just doing external tibias.
Also, how will you sit on the toilet with external femur frames? Or change clothes? Or even sleep? It seems like it would put your hips in a weird positoin.
Once again, I'm not a doctor so what do I know?