you need to figure out your costs- then your time- decide how much your time is worth to you and set a price- then ask for a 50% deposit & determine a time frame & shipping details (if it is a long distance transaction)
some people use a 3X their materials formula--include thread, batting, everything- some set a set 'wage amount' (like i charge $20 an hour to sew for someone) but all the details should be determined & agreed on- with a deposit before you spend a dime on making another one.... in writing is always a good idea.