Cheap low powered Linux

Hi,

Purchase date: this week
Price: 100$ (no monitor)
Purpose: I want to share my OpenVPN connection on a 3g network with the clients on the network + http downloads
Constraints : Low price and low power
Software: Linux so i can go for arm devices also
Options, i know about already: Raspberry pi(out of stock), mk802 ( not proper linux support), Amd E350, Please share the rest
Parts required: CPU . Mobo , Ram and a power supply or a PC on a chip
Location:India
Minimum Requirement: support 3g modem and share Openvpn connection on network so should be fast enough to encrypt and decrypt Openvpn data.

I know this can be done on a nice router with Openwrt but it doesn't have a nice stability and proper support for OpenVPN. Those which have, lie in the same budget as the above specified . Plus this has more upgrade options.

Thanks a lot for your guidance