Don't know the cost at other lofts but I do know for sure that most lofts pay $12-15/hr to their hired help and loft owners/managers very rarely work on small jobs such as yours themselves. And I was told by one such former worker that the best deal would be to hire one of them on a side and get it done at a fraction of the cost as most of them have their own sewing machines anyway.
A few years back while visiting a liveaboard
friend in FL I was present when one such moonlighting guy was measuring up my friend's enclosure which he ended up doing for $1,000+materials instead of the loft's estimate of $3,000-$4,000+materials. And materials were at cost, directly from Bainbridge, which also saved my buddy a bundle. In 5-6 years the enclosure needed just 2 little fixes and is still fine, other than the usual age related wear and tear.