Easy suzie, if they're going to freak out over a loyal customer using MySQL for what it's for, move elsewhere... Even a VPS would be a good idea (as there is no one to tell you what resources you can and cannot use; I recommend WebIntellects.com or PowerVPS.com).
Likely your database is using what, 150 or so mb? If they're complaining, they want you down around 20mb, which will be the majority of your content.
A lot of hosts don't like users using mysql, they have it in their mind that it can be a hog on resources, which is dead wrong (well, miss configured scripts it'll be right, but still).
