The professional-level boards by DGT use RFID and retail for about $500.
I looked into building a competitor some time ago. 64 RFID antennas alone would have eaten up that budget. I believe they do something smarter like having 8 antennas and arbitrating the signals. They have some patents in this area.
I've seen Hall effect and barcode-based systems too. They've always been a bit less reliable than DGT. Actually DGT is not all that reliable: if you are broadcasting a 20-player tournament you will need to manually update the broadcast around once per round. However I think the position detecting (hardware side) is solid and they could do with improving the move detection in software.
None of this is meant to deter you from building this as a hobby project! I think all the approaches would be fun to try.