I know there’s a wide range but what is the average invested to buy and rehab your house flips?

Go to tax lein auctions 1st Tuesday of ev month nation wide...anybody and ev body there...tons of contacts and folks buying property most do need help to flip...ck it out...call tax assessors office in your county...see https://www.pbfcm.com/taxsale.html

Then attached onto the back of that is about 225 deep by 50 wide.

MA and RI vary widely by region in cost and character.

Although attendance varies widely each month, many investors there invest in the US. 

I did walk through it and saw the repairs needed, but its only a single wide trailer. 

Does anyone know of any nation wide lenders?

Opinions on this will vary widely so I'm just throwing out best guestimates but 25% of the GP split or 1-3% of the loan amount if an upfront fee which your investors would ultimately fund through their investments. 

This can vary widely by location, @Anthony Mikolich, but $10k looks ridiculously high.

Don't want to discourage you but you need to go in with your eyes wide open.