Why you should Not buy the cheapest bass available
I judge a School Bass by these characteristics, in order of importance; Playability, Longevity, Volume, Tone, and Physical Beauty. Longevity is the issue here. There is no reason why a properly built bass cannot last for hundreds of years if it is well maintained and not crushed too badly. Unfortunately for the unwary buyer, there are plenty of basses on the market that do not qualify as properly made.
The glue must be a type than truly hardens and yet will respond to a luthier's tricks when a repair is required. Animal hide glue is best, though titebond will do. Many cheap instrument are put together with production techniques better suited to cabinet work, and I have seen outright failure in less than a year, though most often two or three years before the diagnosis is terminal. It is possible to spend hundreds of dollars propping up the imminent failure in this period of time.
It is also important to have an ebony fingerboard. The fingerboard is responsible for much of the necks resistance to bending under the considerable pull from the strings. Also, the surface of the fingerboard is where much of the precision in the set up is applied, and ebony maintains its shape while resisting wear and tear better that any other easily attainable wood. It has no peer.
Good tuning machines are important first because it's hard enough to get in tune at all, let alone having to work with jumpy gears that then slip while you're looking the other way, and second because better tuners stay that way virtually for ever.
Cheap strings are not worth having, and become even less desirable as time goes by. A great deal of the sound of a stringed instrument depends on the string, don't scrimp here. A well made string lasts many times longer too.
The least expensive bass we are willing to sell gets a glowing report card in all these categories. The bottom line is that you won't be throwing your money away, you'll be investing in the future.

What about Volume and Tone and Physical Beauty?
Volume is important because if there isn't enough, you can't be a part of the music. Our school bass has plenty of volume. In fact, You have to spend a lot of money to get more sheer volume.
Tone is another thing. It is hard to talk about and opinions vary, to say the least. It is the biggest difference between inexpensive and expensive basses. The bass we're talking about here sounds as good as any other to the unsophisticated ear, but I'd be lying if I said it sounded as good to me. The sound is certainly pleasing and not at all ugly.
The double bass is a beautiful creation, like the rest of the violin family, and our bass is no exception.