Get both! Get a UPS with a line conditioner. I HIGHLY recommend Smart-UPSes from APC, but they have other line interactive units too, like the Back UPS Pro. Read about them on
http://www.apc.com/ eBay is the best place to find these, but you have to watch for bad batteries, obviously new is a great way to go.
I would get a line conditioner over a UPS if you can't find a good UPS with a line conditioner in your budget. I probably know more about UPSes than anyone on this forum, so let me know if you have more questions.