Minimum $ amount to open a Solo 401K?

[Georges Martin]

I know it's vulgar to talk about money, but as of today I have $25,862.64 sitting in a 401K from and old employer. The returns are horrific. 

It's not much, but I'd like to put that money to better use by buying a rental property within a solo 401K. I read that I would need a lot more money to do so, but why? Would fees eat away at my funds? Do I need a larger down payment? Any and all advice is welcome. Thanks. 

[Mark Nolan]

@Georges Martin

If you don't have enough retirement funds to invest in real estate, you could always invest the solo 401k funds in promissory notes secured by real estate. 

If you decide to invest the solo 401k in real estate and need a non-recourse loan, see following for rules and list of lenders.

https://www.biggerpockets.com/blogs/3441/51027-nonrecourse-loan-debt-for-self-directed-solo-401k-investment