That's a lot of work, don't undersell yourself! I've had that problem and it's no fun!
Do you know what it costs you to make all that? You have to factor everything in: Ingredients, things like paper towels, gas to buy what you need, utilities, etc.
Then consider your time. Figure out about how long it will take you to do all of that, from measuring and mixing, to baking, to decorating. Then pay yourself a decent wage. I don't recommend working for minimum wage, that's no fun either! But start there when deciding what a fair wage for your work will be.
If you're like me, you'll probably be shocked when you realize how much it really comes out to. Unless you're doing this for family or a friend, don't undersell yourself. Working within someone's budget is fine as long as it's realistic. It really sucks to hand over all of that hard work just to realize that another baker would have gotten 2 or 3 times as much to do what you just did.
AHow much to charge is a combination of what it cost you to make it, and then depending on who you are selling it to, what is a fair price. If you're selling to a stranger, then you need to find out what local market prices are and stay in line with that. If you're making it for a friend or relative, it's completely up to you to decide what you are comfortable charging, and what your friend/relative is willing to pay. Nobody can tell you any of those things.