I'm pretty much in the same boat you're in. It took me time to find distributors that had no issue with small sales and that took either check fax of ACH debit. To help you, here's the list of my distributors.
S. Ohio Gun
Williams Shooting Sports
I prefer to deal with Zanders, Williams, and MGE because they have the best prices and most often have what I need to order. Lipsey's, while my first distributor when I opened, seem to be amongst the highest priced. S. Ohio won't do check fax or ACH, but they have one of the best selections of surplus firearms so while there is a demand for them, it's good to have an outlet to get them from.
The biggest issue with some of the larger ones are that they want you to be a stocking dealer and start with a larger purchase and/or have bank references. It's a shame because it seems that the larger ones are the ones that get manufacturer shipments first. I've had an education on the marketplace from the top down since I opened in '09 and frankly, it doesn't thrill me. I'd be happy to share some of the things I've learned with you if you want to get in contact with me.
I set up with Jerry's and the first time I called in to inquire about something small, I got treated like s##t over the phone. Last time I called them.
You'll find that as your list of distributors grows that they do not all carry the same lines of guns. Few sell Sig because of clashes in their business policies. Some don't sell certain makes of guns while others do. I currently have three that sell to me factory direct, SCCY, Bond Arms, and FMK. They seem to be looking for small dealers as well as volume. Smart marketing in my opinion.
One thing I did which I'll never regret is that I networked with a couple of local brick & mortar dealers including a well heeled LE supplier. Once, I had a client that wanted something and nobody had it in stock. I checked with one of the stores I developed a relationship with and they had a couple. They sold me one at cost plus a few bucks and I could satisfy my client. Worked out for both of us. Also, if someone wants something used, I have a place to send him. I'd rather refer someone to someone else I know and have a relationship with than just say I can't help. It does come back to you this way in the long run.
I applied to Sports South a few weeks ago to use them as a distributor, but I haven't heard back yet. I'll have to follow up with them to see what the deal is.
You'll not be able to set up with these guys until after you receive your FFL as they want a copy with your application. Anything else, feel free to contact me.