I'm not sure what urljet does to optimize themselves for vBulletin installations, but surely it can't be better than what a user can do themselves. XD
I use Linode (
http://www.linode.com/ ), and I've been a happy customer for years, now. The cheapest advertised VPS over at urljet is $110 for a single 512MB server with 10GB of hard drive space. Linode will give you a 512MB with 20GB of space on their cheapest plan at $20. (I use that one for my webserver and then a larger one for my database server.)
I guess, though, if you can't set up your server (really not as hard as you'd thnk, tbh), maybe you'd be willing to pay the extra bucks. Heck, I should start selling Linode servers and re-brand 'em with my own name, and maybe I could make a hefty profit. X3