If you are going to go with an unmanaged host, I highly recommend buying your own servers and looking into colocation. If you are going to bother installing all the software yourself anyway, you'll get a much better price.

We were paying $800 a month for two high end servers at LayeredTech in Texas to handle our rails site (about 2M pageviews/day) We then bought two supermicro barebones servers and set up at a local co-location facility in Toronto.

The upfront cost of buying the servers (which were better than the ones we were renting) was $3500, but our monthly fees are now just $160. It didn't take long to pay for the server cost, and we'll have them around for as long as the hardware lasts (I expect it to be a while!).