I could answer your question better with more information.

You may or may not be aware that there is a difference between a purifier and a filter. A purifier is a step up from a filter. Mechanical purifiers tend to be more expensive than filters because they kill viruses with additional chemical action. Filters do not remove or kill viruses. Which one do you need? The Sweetwater is a filter.

Is size/weight a concern? How about capacity? Some filters are cheaper because they don't process as much water before clogging up.

Are you dead set on a pump filter (or purifier?) or would you consider alternatives? Lots of folks here use chemicals and they're cheaper in the short term. I think UV is out for you because it's not cheap.

"Inexpensive" can mean different things to different people. How much do you want to spend?

The "best" unit is the one that fits your specific needs.