Probably the cheapest way to increase your oil pressure would be to use a heavier weight oil in your engine. Another way would be to install a HV oil pump. However, this is a highly debated subject because the oil pump puts extra strain on the cam sensor shaft and has been rumered to break them. If you want to chance it, go with the HV pump. The tried and true way to go, IMO is to get a Kenny Bell booster plate. This is a very nice piece of work and only cost me $26. I personaly saw an increase of 7psi (16-23psi @ idle). The only drawback to this plate is that you must machine out a new channel in your oil pump ( a drimel dril works fine).
BOOSTD