Take this for what is worth from this second level rider and Grand Prix railbird - what keeps a lot of horses from the Grand Prix is the tempi changes. Some Andalusians. but not all, do not have a lot of jump in their canter and this limits the tempi changes. I had a friend with one, a fabulous horse with a little flat and four beat canter and she struggled with the tempi’s. Maybe the horse could have done them with a pro but it was a struggle for her. So if the pro riding this horse is struggling with the tempis it might be really hard for you. Also it is a HUGE climb from where you are as a rider to the Grand Prix. By the time you get there this horse may be older and not as fancy as he is now.
And DO NOT borrow money for a horse. They are not an investment and can render themselves useless in a blink of an eye. Don’t think "Well if it can’t ride him I can sell him for the same price I paid:. Nope. Not if you are an ammie. And like somebody said - if he has been on the market for a year he either has vet findings or is not the quality the seller thinks it is. Not to say he isn’t a fabulous horse. He probably is. Just not a $250k horse.
Have the talk with the trainer. Tell her you really love the horse but he is way over what you can spend for a horse. Maybe the owner will decide they want out and offer him for a more realistic price. And you might have an edge because you have been leasing him and the owner knows it is a good home. I don’t think it is insulting to tell somebody that you don’t have that kind of money. telling somebody the horse is overpriced might be or offering a low ball offer.