Q:

Daily Adjusted Seatpost for Trainer Bike

I just got Nashbar's Ascent Fluid trainer and put an old big-box store bike on it that nobody was using, so now I've got kind of a permanent trainer bike which is nice.
The problem: me and my partner are different heights/sizes, though close enough that all I really want to do is raise the seatpost when I ride, then adjust back down when I'm done. 
Of course I need a new seatpost for this b/c it's too short to go any higher.
My question: is there a risk of damaging/wearing out the seatpost/tube quickly by adjusting it twice daily (once when I get on, then again when I get off)? 
If so, what kind of lube (if that's suggested) should I use that won't have toxic/smelly fumes and be excessively messy/require wipedown every time I lower the seatpost?
I use park anti-sieze for my main ride, but that stuff is nasty/toxic so I don't leave any exposed (on the rare occasion I adjust height).
Should I just resign myself to eventually wearing out the seat tube and/or buying new cheapo seatposts once in a while?

A:

Just buy an inexpensive metal seat post, and if eventually it wears out it wears out. That seems to be your least expensive option. Especially if it's just a trainer bike.
Just lube it up with either a little bit of oil or odorless teflon grease.

A:

If the bike is a cheap one, then a really cheap seatpost must exist for it. Cheap Seatposts are usually made of steel or mild steel, which should withstand the wear from repeatedly adjusting the seat height, so my advise here is, don't worry that much.
Some bikes use a type of seatpost that doesn't have an integrated seat clamp. If this is your case, it is likely that you can even fit a piece of common steel pipe to it, which will result really cheap if you obtain it from a scrapyard.
Another suggestion is, instead of using the quick release clamp, you may like to make a few side to side perforations in the seatpost and using a pin to keep it from going down. This may make a quicker adjustment every time, you'll save just a few seconds. This sugestion is particularly suited if you can use plain pipe for a seatpost.
Regarding lubricant: If it is really being changed/regulated daily, and the post slides really easily into the seat tube, there is no need for lubricant. If the seatpost slides easily, the friction is virtually non existent so there is no need to worry for it. Covering seatposts with grease is advised to prevent seizure of the post to the frame due to galvanic corrosion, but this only happens if the two pieces are left together long enough. So, again, if you are moving it daily and are concerned about fumes from the lube, you are probably fine without it.

