Programming

If you need X months to build this product out so you can sell it, and after that Y months to become profitable so you can support yourself, you need to work out what your expenses are going to be for those months in total, and collect that much money. If nobody is going to invest it in your project (and if they did, I wouldn't recommend taking it, because professional investors are the natural foe of the entrepreneur), you need to come up with that money yourself, which means you need to save it. Basically, you need to plan to retire for a few months.

You need to look at the money you make and your expenses again, and you need the difference to be enough so that you can save up for the project in a reasonable amount of time.

If that math doesn't work, you need to change those numbers: the expenses need to be lower, or the amount you get paid needs to be higher. If you're a programmer with a lot of experience, you should be being paid noticeably more than twice what a human needs to survive, so saving up for N months of eating pasta in a studio apartment in the middle of nowhere doing your project should only take 2*N. months of eating pasta in a studio apartment in the middle of nowhere doing your job. If you're not making that much, your current job is underpaying you, so try unionizing, demanding a raise, or finding a new job to work at a bit before starting your project full-time.

You can also look at options like grants (which are usually available for open-source work, but which might be able to help you end up with some sort of FOSS-based consulting outfit or open-core ecosystem), or going to grad school and turning your project into a research/thesis project done in collaboration with an advisor, or convincing your employer to let you work part-time so you can put in more hours on your project without needing to plan to have zero income.

But, as other commenters have noted, building out the MVP is not really determinative of whether your business plan will actually work. So whatever you do, you will want to make sure you don't have no plan for if the sales don't start rolling in at month X+Y as you'd hoped, and you want to make sure you give enough attention to the business development and sales work that is probably actually most of the problem.