Make sure you aren't undervaluing yourself. You have to remember to account for unbillable hours, like when dealing with your own business but not clientwork. It is likely that 1 hour a day or more will go into this, so up your hourly rate to make up for that.
If a potential client has issues with your pricing and/or paying upfront, he is most likely a trouble client and you should walk away.
Don't waste your time with clients you can tell will be trouble. You will find other, better clients. Don't worry.