Ask HN: How do you host cheap relational databases?

I like building prototypes which might only have less than 10 users but need to be deployed to the public. Often I use dynamodb because the cost of this kind of load is nearly nothing, but because with dynamo you design your schema based on access patterns, I don't find it well-suited to a prototype where the access patterns change all the time. My problem is the relational dbs I've seen cost usually a min. $40/month, which is too much, especially considering I often have 10+ prototypes at once. Any ideas?