Ah, well in that case. You could look for something similar to this EVGA: https://www.evga.com/products/product.aspx?pn=100-BR-0450-K1
450 Bronze 80+ would do pretty much what you need. Decent quality, for $49 USD / £39
You'll just have to find something similar elsewhere since the one on EVGA's site appears out of stock.
To add on to what Axeonelite said. If you don't have a lot of money, and are relying on your parents, I'd suggest one of two things. Look at getting some side-job to make a few bucks, or explain the situation to your parents if they are paying for it (and no, this doesn't mean trying to talk them into one of the most expensive ones).
You need to make sure you get a power supply from a reputable place. ( IE: Corsair, EVGA, Antec, NZXT, etc). And not some weird fishy off-brand power supply just because it's the cheapest. It doesn't mean that you need to buy a Platinum 80+, but this is something you'd be better researching. Because you need to find a reputable website to buy from (newegg, amazon, etc. unless you want to go the route of "used" and get one from ebay") and read reviews, etc.
Buying a cheap power-supply can cause a lot of issues, and you can potentially put your entire PC at risk if something goes wrong. As I said, no it doesn't mean "Hey dad, I need a Platinum 80+ multi-rail PSU". It just means be cautious. Because buying one of those PSUs from somewhere like Wish, aliexpress, could mean that you get something fake / NOT dependable.