I successfully completed my first one nearly thirty years ago.Of note to would-be players: Surplus funds are generated by mortgage, deed of trust and certain types of lien sales whereby the forced sale generates an excess above the secured debt and cost of sale. 

When told that it would cost $X, an amount which the Client deemed excessive, he was asked what he thought the return would cost.  

If you still have questions, feel free to contact me by private message.Also, the answer will depend on your situation and objectives, return requirements, risk appetite, ...

I don't need lump sum, I need excess to equity when I would need, aka HELOC like investment.

Depending on your appetite and means, we may have a deal for you that needs a 2-3 year bridge. 

Anything in excess of 10% is very good.

I am usually for solar, but this one is excessive.

So any one person's answer to the question will be shaded by their own appetite for risk. 

Additionally, you and the seller agreed to handle and shortfall(Yes keep in mind you could have been shortchanged as well) or excess will be handled outside of closing.So, if you owe the money you should pay it just as you would expect the same. 

Do the investor or original owner have an opportunity to recoup these excess funds?