Wait until you see how long it takes to  do it rite. There's a reason more people dont do it themselves.  And a reason we wouldnt do it any cheaper.
I'm working on a new frame for a crf150/250rx with new ztyle trx 90 plastic doing a retro fit with yz80 until I can get to the whole new frame.
Look at availability of parts and the quality of them before you commit to  building something.