Sump filters are very easy to maintain and are very inexpensive to set up... but the initial design and installation is far from "simple"...
The cheapest / easiest filters you can just buy, plug in and go with are Power Filters. The AC 110 very commonly regarded as the best of these filters.
Canister filters are definitely an option but they are more expensive and they do require much more involved maintenance.
There are other forms of filtration some may consider, but these are the three most common approches.