Buy with a credit card through one of the companies that resells grandfathered Google Apps accounts and you should be okay.
Edit: I just remembered reading an article [1] about hooking up a regular gmail account to the free tier of mailgun, so you send and receive through your custom domain but otherwise have a plain old gmail account.
Is there a "reputable" reseller that HNers use? I can find tons of resellers but e-mail is too central to my identity to gamble like this. At least I would be able to transfer my domain again, but if they get full access to my stuff even for a few hours I'm already screwed.
(edit: what I mean is that he can recall the account and get full access to it while DNS still points to Google)
You shouldn't have to hand over control of your domain at any point. You buy a placeholder domain from them, log into the placeholder Google Apps admin settings, add your domain to the account, and then switch your domain to be the primary.
Edit: I just remembered reading an article [1] about hooking up a regular gmail account to the free tier of mailgun, so you send and receive through your custom domain but otherwise have a plain old gmail account.
[1] https://simplyian.com/2015/01/07/Hacking-GMail-to-use-custom...