Abe will run ok on Digital Ocean's 1GB RAM VPS ($10/month). It is possible to get it to work ok also on 512MB RAM if you set up swap memory, pick the right distro and disable some unnecessary things to conserve memory use. Don't worry about CPU usage because even if Abe is written in Python which is a shit slow performing language that is not where problem or bottleneck with Abe is, it will run good on some old Pentium 3 If you want smaller footprint blockexplorer (but with some limited feature) check out RPC Ace https://bitcointalk.org/index.php?topic=686177.0