I order my thc tests through ebay,about $1.20 each.I usually buy 10 at a time.
I would say you're in pretty good shape.I'm a big guy 6'2" 280 lbs and I smoke once a week.I test myself daily and usually by day 4 I'm clean.
Just follow the 3 main rules drink fluids the day of the test,piss a couple times before the test and always take the middle of the piss stream,
Good Luck