Make sure you read the "'Buy a mini' they said" thread here first!
That being said, I adopted my two minis (the ones that jumped out of the moving horse trailer) for the same fees that a full-sized horse cost. Since they ended up being more trouble than a full-sized-horse, and just as expensive to keep, I suppose the pricing was dead on!
"If you get to thinking you're a person of some influence, try ordering somebody else's dog around." –Will Rogers
I want to rescue a miniature horse as a companion for my horse. I wanted to know how much adoption fees are roughly for miniature horses? Thanks in advance.
Many minis that end up in rescue have never been treated as horses i.e. not gelded, never dewormed, never vaccinated, no foot care, no teeth care, zero manners or trust in humans - chances are you can get one just like this for free off your local garden list.
Once the aforementioned mini is at a rescue, you are adopting
Mini's require specialized fencing & often special care to avoid the butterball on laminitic feet syndrome, if you're looking for an easy companion for your horse, find an older horse, pasture sound horse etc.
But also consider that when you take your horse away for whatever, there may be herd (bound) behaviour i.e. adopt 2 minis
If you are in the NJ area Camelot Auction generally has tons of minis and donkeys. Of course, they have to be quarantined, etc., but may do the trick for you--after you read all of the recommended material above.
It will depend on where you are and what rescue you adopt from. We have one right now that has an adoption fee of $100 (I think). She's around 20 and blind in one eye, but she is also current on all vet care and has been a companion to other horses in the past.
If there's not a reasonable rescue near you, check out craigslist. I see minis posted there from time to time.