With the constraints you've stated, I'd suggest doing a kickstarter/indiegogo. That way you can be first to sales at least and you can validate your value proposition and positioning. Being first to sales means you've captured some people. If they only have budget to buy one product and your product takes up that whole budget, then you've locked out competitors from getting that customer.

Feel free to schedule a call with me. I used to work at the McKenna Group, the company where the book Crossing The Chasm was written (before Geoffrey Moore went off to create his own consulting firm)