if you're already using seio's for flow and don't mind more pumps in the tank probably the cheapest way is with 2 or 3 Koralia (4's) or 2 or 3 of the maximods with the $16 kit that was discussed in a previous thread:
http://archive.reefcentral.com/forum...readid=1286743
Tunze's are really nice and efficient and customer service is the best, however they are not cheap.
The other route would be closed loop, but I'm not certain what pumps are best for the cost with this route. Hopefully someone else can chime in.