maxim carries a number of these sensors, and will ship you samples for free. i just got a ds1620 from them.
honeywell makes some combined temp/rh sensors, and will also send you free samples
in fact, if you just search for "free sample IC", you will find that there are TONS of products you can get for free just by asking nicely. i probably got $500 or so worth of free products from a dozen different companies recently, just by asking nicely. if they dont have a "samples" link on their website, just email customer service and explain yourself. i only had one place decline me because i wasnt a hot-shot with plans to buy 1000 or more eventually.