At the risk of an opinionated answer...
I would say that if money is tight, then get the correct printer in the first instance, en lieu of purchasing one that ends up giving you unsatisfactory prints, and that you then have to spend even more money on, in order to get prints of an acceptable quality.
A heatbed, while not essential, is, IMHO, certainly desirable.
Just a thought - Instead of purchasing a ready built printer on Amazon, have you considered building your own RepRap? If you look at a Bill Of Materials (BOM), and then purchase the parts individually from China, then not only will you end up with a good/better spec printer, for the same price, but you would also understand the mechanics a lot better. A good, and thorough, understanding the printer is essential for repairs, when (not if) the printer goes wrong (and believe me, it will). For a little over £200 I have managed to source all of the parts separately for a P3Steel v4 printer, with Kysan stepper motors, and an aluminium 200 mm x 300 mm heatbed.
Note that I knew nothing about 3D printing, three months ago, so you do not need to be an expert, just do plenty of research beforehand.
FWIW, my aluminium MK3 heatbed was £19.99.