How long should pedals last? I use cheap flat pedals, aluminum or plastic. They lasts about a year (1K-2K kms) before dying (cracking noises at each stroke).

I don't mind paying US$10 each year, but it hurts my eco-heart: I want to recicle, to repair and not pollute the Earth.

How long should pedals last? Do serviceable pedals last longer? May I try to repair non-serviceable ones?
Increase your budget until you can afford second hand pedals with cup-and-cone bearings, then spend a few bucks servicing them.

DMR's V8 and V12 models are very popular and have been the same for years. The V12 typically has better seals and lighter materials than the V8, but both are serviceable.

Here's a guide on servicing the DMR V8:
http://steveukmtb.wordpress.com/dmr-v8-pedal-overhaul-cup-and-cone/

I got Wellgo's V8 clones via eBay for 7GBP delivered (about 10USD?). I don't know if they're the same internally but they might be an option if you cant get pre-loved DMRs.