It's pretty easy. Go and pay for a registered valuation - from a valuer.
If this comes back say at $400K. Then sell 50% to your friend at $200K. Your friend will need to pay stamp duty on the $200K purchase price. You as the seller may have to pay CGT on the sale if there has been any CG on the IP since you purchased it.
A solicitor or conveyancer can see to the paperwork as to new ownership on title etc.