Considering the market for Ions not as much as parting it out,really depends on internal upgrades ie bolt,board,detents,I'd say aprox $150-200 max to the person who wants the gun like it is on a good day,that may even be high,stock Ion sell around $75 or lower,just my opinion thou.
the reg itself is worth about $75 if it is a AKA(almost positive)
Looks to be in primo shape,too bad custom Ions arent worth what is put into them,id guess someone spent $500 more or less to build it
If you can/need help iding internals I'd be willing to help
if you ever selll the reg let me know