Need one for my class but don't want to spend too much. Any ideas? Any old one will do, more for learning experience about birthdays

Try Carrefour or Walmart bakery section.

or you can try the local bakery - they almost ALWAYS do birthday cakes ranging from about ¥80-¥+100 (depending on size, etc). And they'll box it, add candles (crappy candles, so gotta be quick), and paper plates and mini-useless plastic forks.

Hi Coco1!

My name is Stefy and I'm the menager of the Box Bar (wenhua xiang)
if u want to buy a birthday cake we can provide for that: all our cakes are homemade:) if u want to come here and have a look or have more info u can call this number: (0871)5362137

thanxxx

Stefy./

The best value for money are Jiahua bakery to my opinion.
Be careful some cake needs prereservation or are sold out quickly.