A cheap bass isn't going to have much spent on materials and won't be put together with as much care.
Everything on your bass is going to affect the tone so a cheap bass will react, feel and sound differently to a better built bass which is made of better materials.
That might not matter to a player so a cheap bass will be a good buy. But if you can hear the difference, and that difference is important to you then you'll probably buy a better built, more expensive instrument.
An example of either end of the scale I'm talking about would be Wish basses and Fodera.