Note that the one on eBay does not include a storage tank nor a sink faucet.
Check Sam's Club. They usually have a five stage Watts RO system for about $150.
http://www.samsclub.com/shopping/navigate.do?dest=5&item=165779 Actually, it's $167. Just don't buy anything that's based around proprietary filters (The GE Merlin system, for example) or you will pay through the nose for the system and the replacement cartridgets.
There's a reason why most RO systems look similar: it's all the same filter housings plumbed together, using the same types of cartridges, feeding into the RO membranes. Heck, you can even buy the filterhousings and brackets and put 'em together yourself and get the same thing.
There are different companies making each of them, but it's all the same design. Some membranes are better than others. I think DOW is a good brand of membrane, but it's been a long day.
The more filters you have before the membrane, the longer the membrane will last since the water is filtered better.
It only takes one broken five gallon water jug in your car to convince you that an RO system is a good investment.
Oh, if you're renting, there's an option for you, too. One of my catalogs has a combination water dispenser/dishwasher air gap unit, so you can mount it in the existing hole in the countertop. It's a bit hard to find since it's not stocked by every company out there, but it's worth it if you need it.