have you tried checking out
Webhosting Talk ? It's where we've been researching, and purchasing, our server needs for several years now without going to the (usually) higher-priced options in the adult space -- some things never change: add the word "adult" to it and expect to pay more.
To that end, we almost exclusively go with mainstream server providers now for both our mainstream and adult server needs. And at very reasonable prices. And if you need full management, most will provide it as a service for an extra $30 to $50 /mn.
Most mainstream server providers do indeed accept adult unmanaged options.