I bought my FX5 from an ebay store for $200 + Shipping. Pond Solutions was the name of the store / seller. Easy transaction, no issues, and I would buy from them again in a New York minute. I buy a lot of stuff from ebay stores. look at the feedback for the seller. If they have a few thousand responses and are like 99-100% positive, you can probably trust that seller. Also, if you pay with paypal through ebay... you protect yourself a bit. I've only had an issue buying something from a shady seller one time. I filed a complaint with ebay / paypal and ebay refunded my money. Ebay stores survive on reputation and great prices and therefore are a great place to shop and save a few bucks. I would just make sure you get a "buy it now" vs. bidding in an auction on something used.
The XP4 comes with media.... you may need to swap out or add some more biological media to it... but it definitely comes with some. The FX5 does not. The FX5 only comes with sponges.
The XP4 is easy to maintain as is the FX5 and the eheim pro. The best of those three filters is the eheim pro, but it's also by far the most expensive filter. The advantage the FX5 has over the XP4 is the volume. Because it holds so much more media, it can go for longer intervals between cleanings. That being said, the XP4 is still an excellent filter and for the price you can't go wrong.
Biological media can go for quite some time... and it just needs to be rinsed with tank water.
Chemical media like carbon will exhaust itself in 4-6 weeks on average and would need to be replaced. Purigen by Seachem (I use in all my filters) is a renewable replacement for carbon. Seachem claims it can go up to 6 months before you need to clean / renew it. I clean mine every time I open the canister. Purigen or carbon keeps the water crystal clear and removes organics which removes any odor. People on this forum will tell you that you don't need chemical filtration, but I personally would not run a filter without it.
The biggest cause to clean the canister is the mechanical filtration... sponges. They will clog with sludge and grime. They can be rinsed many times and re-used but will eventually begin to wear and need to be replaced every few years. The rate at which these clog is determined by how messy Miss Bowser is.
