First you should consider what type of range you need to get? Will a 6v system which will give you about 50-60yds. of clear target identification be enough or do you need to go with a 9v system and reach out a bit farther to ranges of approx. 80yds.?
If you're trying to save every dime possible but still like to have upgradeability I think a 6v M95x SF Millennium system would be a great start. You can take a few shortcuts and save some money by going with a Z48 clicker tailcap and bypassing the ARMS mount for now by using a std., inexpensive scope ring to mount the system -