Ash, there are several consignment stores in MD you can look into. I agree that at 4 yo and put in work your horse probably will change quite a bit (both mine did). So you may look into something used on cheaper side you can use at the moment, and when he stops changing more or less, sell it and get something nicer.
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."