Maybe I should branch out a bit when I'm at Costco - I usually stick to California reds but it sounds like there's lots of good stuff to be found elsewhere for cheaper
Obviously, taste is subjective, but I think most people should be able to find wine that they enjoy in the $5-$10 price range.
It's harder than it should be in the US since many specialty wine stores just don't carry cheap wines and in supermarkets and such, many of the cheap wines are super light bodied (this is just a market selection, it's not more expensive to make a heavy body wine) so if you're not into that, you might have to go through a few wines you don't love, though I personally can enjoy drinking wine that I don't totally adore, so I don't terribly mind that.
I would definitely give Costco's Kirkland brand wines a look, they are good value and if you find something you like there it will be pretty easy to get more of it (which is not always the case with wine).
The best value is always going to be buying directly from small wineries, but I have no idea how relevant it is in where you are.