I just started a post the other day on the steriPEN. I have used the PUR Hiker filter for about a decade and carried iodine or tabs as back ups. That has some great feedback on that item.

The flow of your posts leads me to assume, perhaps incorrectly, that your looking to do this as inexpensively as possible. Buying a $100-$150 SteriPEN set up may not jive with that philosophy. That leaves boiling which is time consuming and fuel consuming if you have to use gas instead of timber due fire restrictions. Camping gases for that long in the back country can be heavy.

So that leaves for cost, a filter. I think name brands are the tested way to go for consistency and efficiency but I found a UL filter by Timberline Filters that is only $20 and claims to block out all the usual suspects.