I actually own the z25 it's sitting right next to me. If your looking at a big price difference for minimal gain in quality I'd just get the z25 b/c it works great for me and has good quality. Only had one problem with it ever, just ran the option to clean the print heads and BAMM! Note that I am not a printer genius I just know that my printer works good.
A printer is one of those things where you really get what you pay for. That being said, I've heard many say that lexmark is like one of the worst brands. After a brief affair with epson I'm back to being an hp printer user (epson printer died 3 weeks after my warranty expired).
I have a Lexmark E210 laser which works really good, it is basically a rebranded Samsung though. The only problem with 'bargain' laser printers is that they usually only come with a half full toner cartridge. Most of Lexmark's printers are crap though, but it seems like these days, most consumer printers are crap. I've had Lexmarks, Epsons, and Canons all go to hell on me. Never had a problem w/my old Tektronix or HP printers though. I think Epson still has the best print quality, but all of their low end printers seem to be really flaky, especially since the print heads are part of the printer and not part of the cartridge.