As lagopus pointed out, proof testing is not expensive. But the real cost is what is termed "carriage", the money you must pay to someone in England with an import/export license. This cost me about $400 several years ago.
At the time I had sent my Warrilow to be reproofed it was legal to ship an antique (pre-1898) direct to the proof house. The Proof House however (Birmingham) did not have an export license and refused to return it to me. I had to get someone to do it and pay "carriage".
About $50 to send it insured, about $50 to have it re-proofed, and about $400 to get it back....priceless.
