If you want to buy 10 apples at 30p an apple but only have £2.70 you have two options.
You can firstly earn more money or find some cheaper apples.
Now it may be possible to find some cheaper apples at first, but what if you want and need to buy 15 apples and still only have £2.70 and don't want to earn more? Well you may find those 15 apples eventually but it will take much longer than finding 10, the quality may drop and you will have a limited variety to choose from.
Wouldn't it be better to just earn more money?
If you earn more you can buy 10 apples, 15 or even 20, keep the quality high, choose a wider variety and keep the effort low.
At the moment your trying to buy 10 apples at 30p each with £2.70.