The most economical is almost certainly Polar Pur . It does not have the overbearing aftertaste of traditionaliodine tablets as it is concentrated pellets that release a set amount of iodine into the liquid. You then pour x-number of capfuls of the iodine-saturated water into your untreated water, based on temperature and current pellet concentration. (This is MUCH easier than it sounds. You look at a little heat-sensitive scale on the side of the bottle and it say "add x capfuls per liter".) I knew AT thru-hikers who used only 2 or three bottles for an entire 6-month thru-hike.

I prefer Aqua Mira, a chlorine treatment in which you mix 7 drops of treatments with 7 drops of activator (in the little bowl on the cap) for each liter you wish to treat. Then wait 5 minutes for it to activate. Then add the now-yellow solution to your water and wait 15 minutes. The taste is preferable to any amount of iodine and it is quicker than the 30 minutes for them.

Chorine Dioxide tablets have become popular as a back-up. The only real issue is the wait time. You are supposed to wait a full 4 hours before drinking with them, though I hear this is to kill the spore cryptosporidia only, while most other "cooties" like Giardia Lamblia die within half an hour or so. Still, the packaging is very clear that if you don't wait for the full four hours, you're taking your [legal] life into your own hands......

To remove silt and the like, you can simply use a bandana then treat with the listed chemical treatments. Or you could use one of these Steripen Prefilters which I have been very impressed with for coarse filtering.

If you're looking into filters, you're losing out on both weight and cost, but there ARE times when they may be worth it. For me, in very hot weather, I will carry so much extra water to drink while my new water is being treated that the filter was often worth it. But recently I have found I prefer the Steripen Adventurer, a UV water treatment tool. However, I won't go into details because the cost is definitely on the upper end of things.