I kinda hinted at this idea earlier.... but I'll say it
If you are just doing easy recreational diving...not too deep, using 80 cubic ft tanks or similar, etc..
and especially if you're diving off tourist charter boats frequented by both new and experienced divers (where they drop you on a site, with a plan and rules... the dive is x minutes...or be back on the boat by 3PM or whatever)
then a computer really is not necessary
You'll run out of time or air before you'll get into problem
***that said, I'm NOT saying that you should dive based on old tables and I'm NOT saying you should dive without a computer****
just that it's not really such a critical piece of gear if you're on a budget and any of them, even low cost ones will tell you what you need to know.