His commissions included stamps on space exploration for the United States and the United Nations postal services, official space shuttle paintings for NASA and more than 25 covers for Popular Mechanics magazine.
Other expenses include stamp duty, or transfer tax.
The tax should be resurrected to apply uniformly to all states in place of all other taxes, including stamp duties.
Devolution of property tax receipts, including stamp duty and business rates, would take that figure to around 12%.
The average new mortgage there is 110% of the value of a home, because lenders are happy to finance all the purchasing costs, including stamp duty and fees.
He said the coins are meant to ease the use of vending machines, including stamp machines in post offices, and in some mass-transit systems.
Convention center officials are now projecting 200 national, regional and local conventions, trade shows and meetings in the first year, with 250,000 visitors expected, including stamp collectors, fencers and math teachers, Shriners, Asian-American hotel owners and two Muslim groups.
Danny Cox, from independent financial adviser Hargreaves Lansdown, says: "Prices aren't rising everywhere and transaction costs to buy are very high, including stamp duty, legal fees and estate agents' fees.
But the Neath MP said he was in favour of devolving some taxes, including stamp duty and air passenger duty.
