I haven't rented any space in a while but I'm going to assume $400/month is about the cheapest that you would be able to get a half a cabinet.
And of course, that depends on how much bandwidth you need, how much power you need, are you running top-tier connectivity or something like Cogent/he.net...
A VPS will be cheaper, easier, and better in /almost/ all ways.
1U rack space, including power, a 1Gb network uplink, and at least 1 dedicated IPv4 IP, is going to be at least $60-80/month, and even that would from small discount colo providers you have never heard of.
