Best way to handle renovation C of O?

20 years ago, my ex and I combined two apartments in a co-op, with board approval, a certified architect, etc.

For some reason lost in the mist of time, we didn't get a revised C of O, though the apt is up to code, etc.

Now we're selling the apt, and we learned there's a simple way to revise the C of O -- a Directive 14, where an arcitect self-certifies the renovation with the Dept. of Buildings

The original architect no longer works in NY. Should we hire the co-op's architect-consultant to do this? Should we hire an expediter? It seems relatively straightforward (French doors were put through a wall, and kitchen fixtures were removed to form a bedroom, with gas capped -- that's it), but we've no idea whta the costs are. A couple thousand we could swing. $10,000? We'd be screwed.

Anyone have any idea what this Directive 14 should cost, and whether an expediter is the way to go?