Do NOT put faith in an "oxidizing adulterant like bleach or hydrogen peroxide". This is an old wive's tale with no basis in scientific fact. It probably won't matter much on the type of piss test your parents are going to give you, but in a higher end test you will be discovered and the consequences of tampering with a sample are usually worse than a positive result. It's easier to argue a false positive than to explain away a tampered sample.
I know you said that you can't afford a good detox, so you're going to be very limited in your options. THC is stored in your body's fat cells. A thin person might be able to drink a few gallons of water, do some aerobics, and pass a piss test in only a matter of days. If you're a little heavy, though, it becomes much more complicated. I've actually abstained from smoking for 60 days and still failed a piss test.
So there's your first option....abstain from smoking (just for a lil while), start drinking lots of water, burning off any new fat. Some people believe that "adding a new layer of fat" on top of the old layer of THC-infused fat will temporarily mask THC levels, but I've never put much faith in that.
The next best option would be to keep a clean sample handy. I've been through enough BS now to know that it ALWAYS pays to have a clean sample within arm's reach. Who wants to be walking around with someone's piss in their pocket, though, right? So what I've been doing for years is ordering powdered urine from some well-known web sites. If you decide to go that route, when you order the urine kit, you'll usually receive a 100cc "specimen bottle", as well as a tiny vial of super-concentrated powdered urine. Keep the specimen bottle filled with water at all times, carry it on you. Keep the small vial of powdered urine somewhere else handy...they're usually small enough to fit into the "change pocket" on a pair of jeans.
Unless someone's going to stand over you and watch you piss into a cup, the powdered urine kit is foolproof.
Apart from that, though, you're in a tough spot. We all love our favorite medicine, but there are still some circumstances where the only option is abstinence. Don't worry, though, once the smoke has cleared...weed will still be here
Good luck
