My favorites and in this order are:

Snyders - http://www.snydersantiqueauto.com/modelaparts (Good all around, you talk to the owner if you call)

Brattons - http://www.brattons.com/ (You need to request a catalog as they keep missing their deadline for an on-line version

Mac's - http://www.macsautoparts.com/ (They supply many of the parts to other Model A suppliers)

LeBaron-Bonney - http://www.lebaronbonney.com/ (Slow shipping tho good quality stuff)

Their prices are all about the same, though if you have a roadster, LeBaron-Bonney top irons are much cheaper and are most likely made by Girtz as are everyone elses.

As the owner of a Brookville '30-'31, I can unequivocably state that they rank at the very bottom in quality and customer service.

None of these parts are particularly cheap - but working on older cars where they are no longer mainstream, and have a limited parts turnover vs a good inventory can be expensive - simple economics. If you aren't willing to spend a few bucks for an "old car", sell it to someone that cares, buy a new(er) car from a dealer then trade it in when it gets worn out or you get tired of it, for another one.