We worked out of our homes while we finalized the design and lined up suppliers. During this time we searched for some affordable manufacturing space. We settled for a section of an older building and negotiated lower rent than what was asked. Bootstrapping means making do with what you have, and reinvesting your sales revenue in more equipment and inventory as your customer base expands. Some amount of up-front money is required and the amount will depend on what your product requires in the way of machinery and raw material to get it produced.
Used machinery can be a bargain and material prices can vary widely depending on supplier.
During the startup phase of your operation, you must watch your cash flow very closely, and question every expenditure. The best advice I have for the startup entrepreneur is not to buy anything before you need it. Even if it's something you know you'll eventually need. Wait until the requirement is immediate. Obviously, lead times must be considered for certain things, but don't purchase goods and services until they're essential to building and selling your product.