No, heroku has a postgres service where you can create as many free dev databases as you want. These have no size restriction, just a 10,000 row limit and 0MB cache, as well as some other feature limitations.

You can add as many free dev databases as you want with a single account AFAIK. You aren't limited to one per app, account, or plan.

PayPal lets you generate one-time use credit card numbers, don't they?

Only in the US.