Boy I hear ya in the expect the unexpected!
2 years ago...July 3rd 2010 to be exact. My daughter and I were going shopping, thought we'd stop in first and check on the horses. Much to our horror we found our dear mare Cinnamon favoring her back leg...then we discovered why...
She had rolled and got her hind foot hung up in the fence and tore it from the center of the frog up over her heel and into her pastern.
It was ugly and bleeding profusely.
Instant change of plans! Off to the vet we went. Which that in its self was no easy task as we had to borrow a horse trailer from our neighbor who wasn't home! I left her a message and said...I'm taking your trailer!!
She had to be completely put to sleep, stitched and casted!
She healed perfectly, but not without a lot of maintenence and care and the funny part of this story is the cast...
So just from the first visit, it was $1000.00. Then of course the wrapping supplies and meds I was just tapped out. When it was time to take her cast off...I didn't have the money left to get the vet out to have it removed. So I thought I'd do it myself and save the few hundred bucks.
Of course I didnt have the proper tools, I had never seen a cast before and I THOUGHT that the hard outer shell was thin all over, like it was at the top. So I started nipping it with hoof nippers and it was working great...then the cast got THICK, like 1 inch thick...and I thought...OH MY GOSH! I got a very sharp little knife and started cutting through the layers...I kid you not...4 hours later I had made progress but not enough to get the cast off.
I thought...oh this is going to be bad...I mean, here I started to remove it...and now I'm stuck and I'm too embarrassed to call the vet out to have it done....what am I going to do???!!!
So I let her loose to go run and play and hoped with all that, she'd get it to come off...but the next morning...her cast was still on, solid as could be!
(I have pictures documenting all this)
Then I thought okay...if it's too thick to cut through, then I'll just have to make it thinner..and I got out the hoof file and started rasping the cast away.
Needless to say, she's an amazing horse, she stood tied for another several hours while I rasped and rasped away...I learned that a cast isn't easy to remove without the proper tools, but it CAN be done with a hoof rasp and hoof nippers.

Although..I really don't recommend it! LOLOL
I still have the mangled cast. I'm rather proud of my accomplishment. Our cinnamon is sound as can be and had no lasting affects from her injury.
I don't know if you have it..but in our area most veteranarians accept it and that's Care Credit. It's saved us time and again. It's basically a credit card for medical/vet bills. zero % interest if you have it paid off within the promotional time limit...which is usually 6 months or 1 year depending on the amount charged. My credit score wasn't great when I applied and I was approved for 1500.00! I was shocked. My credit limit has increased to over $2000.00 now and it's a fabulous piece of mind I tell you what.
Good Luck with your guy...you are doing the right thing for him
Toni