Casting runs roughly $800 to $2,500 including the rechecks and re casts; surgical repair runs $2,000 to $12,000 depending on complexity. But the comparison only exists for the minority of fractures where casting is genuinely appropriate: stable, well aligned breaks below the elbow or knee, mostly in young animals.
The trap in the cheap option: a cast on the wrong fracture buys weeks of discomfort ending in a bone that healed crooked or not at all, followed by revision surgery that costs more than doing it properly once. Bones heal in whatever position they are held, and a cast cannot hold what it cannot control.
The x-rays answer this question in minutes, and any vet quoting you for either pathway should be able to say plainly why your dog's fracture is or is not a casting candidate. If money is forcing the cast conversation onto a fracture that needs surgery, ask about the amputation alternative too; it is a kinder outcome than a failed cast.
Send what your vet said and quoted. A veterinary surgeon reads it and comes back to you with what they can do and what it would cost, before you pay anything. A written second opinion is from $250.
Send the case, hear back from a surgeon with what they can do and what it costs, and only pay if you go ahead.