I'd second paying with cash, much cleaner, esp. if you haven't worked with your coders until now.
Granting equity should be done with great care as it means entering into a long term relationship, very much like getting engaged.
You could mention that your goal is to grant equity to them, provided you are satisfied with the results and there is mutual interest.
... but you should definitely test things out first with a paid work engagement.
If cash is not an option, I would not value 1 month of work at more than 1% of equity, assuming a valuation of < $500K at this stage of the game.
Consider playing around with a vesting schedule to foster a long(er) term engagement.