Are you in the industry for your product? Is there anyone in the same industry who knows you and you could convince there is a market for your product? Someone to be your co-founder and help you create your demo?
What about just proving the market exists? Can you get surveys, interviews, testimonials from buyers in the industry that they need this product and would by $X for it? That would go a long way to convincing someone to get you funding to demo.
Can you MVP a simpler version? Something that only costs $50k instead of $150k but proves out 80% of the functionality?
As a founder, you will face this type of problem constantly. You will always be short of time, money or talent (or some combination of all 3) while trying to make your goals. When someone invests in your idea, they are as much investing in you and your ability to navigate these challenges.
Bringing a real MVP to market and making those first few sales is a huge proof of concept for YOU as a Founder. Investors need to see that.