Hi, welcome to DakkaDakka

Yours are metal?
These are Dwarven pony carts. There seem to be a few variants. Two were in a 10 figurine Dwarf Miner set which I think was metal and released in 2006 or 2007. These are as far as I know not really rare.
I found this image
Here is the 1991 Catalogue but I did not find one in there, maybe you have better luck.
http://www.solegends.com/citcat1991b/index.htm
Also there was a plastic one in the starter set Battle for Skull Pass released in 2006.
The plastic one should be widely available, not worth more than 2 or 3 US$.
The metal ones
afaik are not rare, too. The ponies were used for either battlefield decoration, mission markers or as unit fillers in regiments.
Yours if metal could maybe be sold for 5 - 8 US$ but only if there is currently someone interested in it looking on e.g. Ebay. 1991 items if auctioned approriately could make a bit more. Add 1991, oldhammer, metal, dwarf, warhammer and
OOP to the auction so interested people will find it.
Check the Bugmans Forum (a fansite) and offer it there first. Maybe they will react quite interested. Collectors of this stuff usually dont pay insane prices, but it wont end for 0.99 on Ebay either. Give it a try
www.bugmansbrewery.com
I hope this helps, good luck Curious Guy