I guess the advice should be: start a spreadsheet if you're curious how much financial pain you are able to endure! The prices go up exponentially if you are constantly saying, "while it's this far apart" or similar. Another plus for Swarf's get a plan and evaluate first.
Minto, funny about having your son do the purchasing. My Dad did the same with me when he was building his Moto Guzzi Eldorado. I almost felt like a double agent.