Concentration of degenerate primers should you dilute to?
You can just add 2µl from each working stock (10µM) to your PCR mix of 20µl.

You can check this protocol. 
Caution: The author has used $l$ instead of $\mu l$

He uses 5µl of each primer (20µM) in a 50µl reaction. This is double of what I mentioned. IMO it is best to try with a lower concentration and then increase it if necessary. Excess primer concentration can give rise to some nonspecific binding and amplification if the primers are not perfectly designed. 

From this site:


  Using degenerate primers
  
  Because a degenerate primer is really a mix of different primers, only
  a fraction of the degenerate 'primer' will actually work in the PCR.
  One would therefore need to increase the primer concentration in PCR,
  sequencing reactions, etc. If a primer is 8-fold degenerate, the
  concentration should be raised 4-8-fold, and so on. However, for
  higher degeneracies, e.g., 64-fold, one cannot increase the primer
  concentration 64-fold and would have to try their luck with a
  5-10-fold increase only.