I got an oxygen stone that feeds from a small tank from Lowes and Home Depot - the whole setup when you factor in the tank will cost you between $40 and $60. It's pretty nice, but you need to be careful that you don't add too much O2. To be truthful...once my last tank ran out, I have not used the O2 stone for about a year...but they are really convenient, esp. for big beers.
I think 30 seconds on a normal beer, and a minute on a big beer will give you the results you need without over-oxygenating.