Nothing is etched in stone in any transaction, negotiation always comes into play. Where you are, dare I say who you and/ or your trainer are and the specifics of the horse, term of the lease and what both sides want can affect the deal. So its hard to say any public “ standard” exists.
On top of that, advertised prices are just that, advertised prices. Unless you are in the room when the check is signed or see a copy of the wire transfer? Nobody knows what really happened. One side puffs up what they got, the other brags on their negotiation skills in driving down the price…and…we all know… actual cash received can be inflated to boost commission by less savory trainer/agents. As does reducing price if it stays in the barn, sometimes disclosed to outsiders, often not.
Overall everything with horses has gone up, yet another reason to deal only with those you know well and trust. Not just because if a recognizable name
OP never said if they were talking about Hunters or Jumpers. There can be considerable in the price for similar age, condition and level between these.