I'd say your best bet is to buy some old used plates from a local used sports equipment place.
Here in the States we have one called "Play It Again Sports" which has weights and bars and just about everything for a steal.
Other than that, and this is a serious recommendation...
Get some sand at the local builder/suppliers, put it into contractor trash bags in 25-50 lb groupings, seal with duct tape, and place them into an old surplus Army duffle bag.
Now, with this set up, squats take on a whole new dimension. Once the bag is up on your back, squat using good form.
The sandbag you've made won't cost you that much, but will benefit you far more than anything else, and you will be able to use it for presses, snatches, rows, you name it.
Eat alot of vegetables, though. Your bones will need the minerals!