5% coverage means if you add up all the black area you print on your A4 paper, it will take up 5% of A4 size.

I think it's a waste of time looking at how many pages a toner cartridge can print. Most of the time this is quite standard already. For eg, some toner can print up to 5000 pages but that's because it's bigger and it cost more. Printer market is so competitive now that nobody is so much better than other.

So, if cost is such a big issue for you then just get a low end printer of any brand will do. I personally would go for HP (for it's BRAND reliability) and OKI (for it's new lifetime warranty LED printer).