if your concurrent users are below 100, then any shared hosting will do, I have experienced myself running moodle on shared hosting without any issues, i have personally tried moodle on Bluehost/Hostmonster (Both are same group) for less than $5 a month. So you'll better be with a Shared Hosting provider than getting a VPS unless you are getting a premium level VPS account.
If your needs are crucial to get a VPS, then give a try to wiredtree.com, they have their VPS configured on SSD's, so you can expect performance to be outstanding.
also, if you'll consider getting VPS with wiredtree, do as well consider getting webserver to be upgraded to lightspeed web server for $12 extra, still you'll get a better deal as compared to dreamhost.
another very recommended VPS hosting provider is "A Small Orange" asmallorange.com, their plans are comparable to wiredtree.com in price as well, but have heard very good reviews about both.