As long as you're a crew member, and can prove it with your card, you shouldn't have any problem entering, exiting and reentering Thailand on a very frequent basis.
if you know how ED visas work, you'll know they'll be doing more profit on it, as you'll need to visit Immigration once every few months. On a DTV, you might not even need to visit Immigration once in the whole 5 and half years, so it's a "loss" for the agents.
As a matter of fact, the time the OP has invested writing and reading the email to the agent might be even more than 15 minutes, what it took to send my DTV application
this has nothing to do with being able to afford it or not. I'd be able to "afford" hundred of agents, but I refuse to. Come on, I didn't even spend FIFTEEN minutes on filling and sending my DTV application online 🤷🏻
IF it was a super long and/or complicated process, then yeah, I'd be the first using an agent.