There is so much information about how to successfully ground grow material these days from places like this forum to Brent at evergreengardens that growing your own is a very economical route financially if not in terms of time/space.
It's kind of like an investment fund that will bring dividends in the future hopefully when you have the skills to do it justice.
The Acer air layering thread is another great example of people being creative with propagation and by doing so they also invest in themselves:
Confidence & knowledge to produce their own raw material. It saves money. Skills develop faster as you now have multiple pieces of stock to practice wiring, root work, branch development etc on. You are more likely to experiment with advanced or 'alternative' techniques safe in the knowledge that you're working on a 'freebie' and there's more to come if this one doesn't work out. The learning curve is proportional to your day to day work with trees, all things being equal (like talent and common sense!) Being able to develop your own stock, therefore, can accelerate your own development as well as your trees.
I love developing my own bonsai from scratch - not because it's the 'American' or 'British' way or I'm just tighter than a duck's arse but because it's friggin fun and a challenge and ultimately more satisfying - every cock up or positive feature is my own. I am not constricted by another's vision.
Anyway - end of passionate diatribe about developing your own stuff - I'm off to check my Arakawa air layer in the sun and make a brew