Custom Mouth Tray For Whitening For Cheap?

I've been thinking about getting my teeth whitened while I'm here in Chiang Mai. Back in Norway the prices are insane.

So-called "in-office whitening" however is out of the question. For the sake of the procedure being quick the whitening solution is way too strong, often leading to a lot of sensitivity and gum burns. A lot of people think it's the most uncomfortable and painful experience of their lives.

I'd like something I can control for myself. Since I'm not in a hurry to get white teeth in an hour, I'm fine with a slower and more gentle solution. When you're in a dentist's chair with his fingers inside your mouth and a lot of money invested in this procedure going well this one time, it's much harder to abort if you feel pain than if you chill out at home knowing you can try again tomorrow without having to pay for the whole procedure again (or at least having a lot of hassle talking the fee down). A tray is also reusable, great for the next time a whitening is needed (teeth don't stay white forever), making rewhitenings practically free.

I've done some googling, but all I can find are expensive packages requiring several followup visits which in total ends up costing almost the same as an in-office whitening. I don't want hand-holding through the process, I just want the tray.

I clearly remember a guy here in the Chiang Mai subforum mentioning getting the tray made for below 1000 thb, I couldn't find it when I searched however. I'm fine with getting the tray made for below 2000 THB.

Does anyone have any suggestions about where I should go to get the tray made?