There are lots of resources today where you can cost effectively build a MVP for a b2b platform without needing to raise lot of funding. In most cases ( as long as you have a great network of investors) you will probably need to have already developed an MVP, validated the product/service offering before you approach. Depending on the kind of B2B platform, you might be able to leverage existing frameworks to help build an MVP.

I have had lots of experience in B2B & B2C platforms and would be happy to share thoughts/feedback.

Cheers