Out of curiosity why do you think fiber will be too expensive?

Indoor/Outdoor Multi-mode fiber is often actually cheaper than some copper. If you're looking at doing the fiber pull yourself then that makes it all the better. Just a couple things to make sure of with fiber: first, make sure you're doing straight pulls so you don't end up with kinks. Second, strip back the outside and tie your pull string or fish tape to the kevlar. This is extremely strong and it won't stretch or cause snap backs if you have a hard pull.

After you've pulled the fiber you just need to find the right company that knows what they're doing to terminate the fiber. People who do it often and know what they're doing don't really charge much more for fiber termination than copper. Terminating 4 strands should only cost about $150 if you find the right contractor.

So even on the slight high side a 1000' spool of 6 strand Indoor/Outdoor fiber at $600 plus the $150 termination fee. You're only in it $750 and will have an extremely reliable connect and another 4 strands should you need more connectivity in the future.

Don't let fiber scare you away, it's not as scary as people like to make it.

Why would 100ft be too much for copper?  Standards dictate that the max for 4 pair wire is 100 Meters or roughly 330FT.

If you want cheap just use two or three small switches as a repeaters once your in the other building.
         200ft of outdoor cat5e - $80
         1000ft of regular cat5e - $100 (might have this already I know I do)
         3 5 port switches - $60 (could be less with a good deal)
----------------------------------------------------
         $240

Just document the crap out of it so people aren't scratching their heads later wondering how a run that long is possible.

Wireless is probably easier but I have had mixed results with some of the outdoor links (the ones I have used are sensitive to power spikes)

Not just power spikes, with wireless. You have wind (particulates), rain, trees,...then there is aspect (which determines what kind of antennae to use ...ie gain needed, deg of coverage). I agree with kagenokaze. Wireless would definitely be more expensive.

The cost of the fiber is not the only cost to consider, the cost for the endpoint cpe must be figured in as well.

The enterasys point to point we had placed was well under the cost of the two switches and the fiber run we would have needed to accomplish the same run via hardline.

The blackbox short haul modems are the perfect solution for a run of copper longer than 300 ft which is what they were designed for.

You could go with kagenokaze's suggestion but if this is for a business environment you will save yourself (or others in the future) alot of headaches by using buisness class (or better) equipment today.

You can buy pre-terminated fiber which you can run yourself through false ceiling etc.
The expensive part of fiber used to be terminating it.  Fiber is fairly cheap now.

If buildings are only 100ft apart you might get away with 2 cisco wireless access points configured in wireless bridge mode.  Line of site lasers would be a better but more expensive solution.

CAn you throw a fiber from one building to another (early on a Sunday morning !)

Have not implemented yet.