Go to the stables

The stables are a big structure, with wooden beams, hay, and rustic fences. Your nose is invaded by the smell of the horses, some of them are sleek and swift for riding, others are more muscular for draft and labor. The people working here are busy.

You check the prices and they are around fifty gold for the cheapest horses. The big horses... A hundred or more. You only have a few coins in your sack...
You have to think about other options

A group of horsemen are selling horses for 4 coins or less, you can afford it, but there is something wrong with them... One of the horsemen notices you and says "We’ve got steeds for less than five gold" The deal stinks of stolen goods or worse.

You can use your magic. "Charm person" is a simple spell and you can affect the mind of one of the sellers to give you the horse for free.
Or you can just steal a horse. The people are too busy, a they will notice you when you are far away.

It's your choice:
Ask the shady horsemen, they seem dangerous, but their prices are affordable
Use your magic to charm a farmer, their dumb brains are no match for your magic
Steal a horse, the security is low, and they are busy with their chores