You might be thinking of getting a small safe. They can be obtained from the DIY sheds at under £100. And for guarding a small amount of cash or those frequently nicked items like iPads they’re perfectly fine. (Although if you’re thinking of protecting a few important documents against fire you’ll need to up your budget to over £100; and even then you’ll only be getting an hour’s fire safety.)
Assuming the former though, you ought to be able to get some security for under £100.
However, it turns out that many people ought to be budgetting for three times the cost of the safe. Just about all of these cheap boxes from the sheds are electronic digital. Many people pay no attention to the battery low warning. Many people leave the mechanical override key — if you’re lucky enough that such a thing is even provided — in the safe.
So they’ve bought the safe. They then have to pay a locksmith to open the safe. Which will be a destructive opening as it won’t be worth the extra cost of picking open the safe and fiddling around with the electronics to recover the now-lost-since-battery-completely-exhausted and chinese-manufactured-and-completely-unrecoverable code. So they then have to buy another, new safe.