$20-30 seems reasonable given you've fed them and kept them warm for 4-5 months. I'm sure you can find someone who has done the calculation re cost of raising them down to the month and week but it does lead me to wonder what your goals are here. I'm not sure there's a financial benefit. I assume it's to cover the minimum for an order of hens? If that's the case it may be worth posting locally on social media and CL to see if anybody wants to go in on an order with you. That way you can get breeds that someone actually wants and then also avoids you having to deal with 10 extra pullets if you're not successful in selling them.
final cents I'd throw in the bucket....the more colorful the breed and egg color the more eye-catching for would be buyer...If it was me I would aim for colorful eggs