Great question. I wrote the book Lean B2B: Build Products Businesses Want to help entrepreneurs get from idea to MVP to Product-Market Fit. I also built a few B2B startups (Flagback, HireVoice, etc).
There are a few things that make this a challenge:
1) MVPs are typically much further along the process in B2B than in B2C. In B2C, entrepreneurs find a market, identify the problems and build a MVP. In B2B, entrepreneurs find a market, find the stakeholders, identify the problems, validate a solution then build a MVP. Customers are less accessible; it takes time to get on their agenda.
2) Investors typically don't want to fund early sales and MVP development in B2B. It's "too risky"; they'd rather come in when the company has a wee-bit of traction.
3) The whole process from inception to early traction and MVP can easily take more than a year. You need sufficient runway to survive.
Although I agree with Jeff, Shaun and Suresh that you can build early MVPs on the cheap, it's important to remember that your initial objective is to convince 5-6 businesses to commit to purchase your solution when it's ready.
To that end, a vision and early mockups can be enough.
If you need money to get to MVP, I suggest finding angel investors, but don't expect your MVP to be the actual product. Everything will change.
Feel free to reach out if you'd like to talk about this.