Help with horsey problems!!?

Ok, so I have been riding for 10 years, and I really want a horse of my own. My mom is chill with that, as she was a racehorse trainer for 20 years. The only problem is that When she was training 20 years ago, a $2,000 untrained horse was DAMN NICE. Well now, I can get a $2,000 horse that is well trained with a lot of hidden problems. How can I convince her that a $4,500 is NOT that bad for a 16.3 Quarter horse (yes, quarter horse, not one other breed in his pedigree) that has been trained training level dressage, and 100% SOUND??