How Much Should I Ask To Compose A "simple" Music As A Birthday Present?

A close (very close) friend of mine asked me to compose a piece of music based on Beethoven's "Für Elise" as a birthday present to her mother (her name is Elisa, a portuguese version of Elise). So, I'm thinking on composing some sort of variations on the bagatelle, but I don't know how much to ask!! After asking me the music, she (my friend) asked: "How much is it?"...

I simply don't know.

Can you guys give me some ideas?

I can't ask for much money as it's a "simple" present to a close friend of mine... but I simply don't have parameters...

(my currency is Real, brazilian, but you may use Euro or Dollar for references :P )

Can't you just write a nice piece for your friend's mother without charge out of the goodness of your heart? Seriously that is what you should do.

I usually charge close friends about half a pizza.

Well, she asked me to pay her, it's a present "as any one she could buy at a store", but it's a music! She wants me to get payed for it :P

Charge fairly for your time.  Figure out a rate of pay for yourself that you would be comfortable with for a commission from a local symphony who wanted to commission a piece.  These things have a way of coming back to bite you later otherwise.  Some OTHER friend will hear about this and decide it would make a great present for their mom too.  And another one after that…  If you don't charge fairly for the first one, it is very awkward to have to raise the price for the next one.  And work for friends always ends up taking longer and taking more care than work for the commercial world.  Because you want to be very sure they are happy with it.  And because they are your friend, but not a symphony orchestra director who is used to commissioning work, they feel very comfortable asking for you to change what you have written, and change it again, not realizing what a pain that is for you.  And you have to be extra nice about it, because they are asking you to do this, in part, because they love you and want to be supportive.  

You buy presents.

You give gifts.

I'd compose the piece and then give it as a gift free of charge.

Don't take payment for something like this, it defeats the principal of it.

But then it's not the friend's present to her mother, it's Perrotta's present to his friend's mother, and the friend has to find something else to give…  Friends of mine buy my pottery all the time to give to other friends of mine, but they do want to buy it from me.  That's part of the present.  "Hey look!  I supported our mutual friend's business!  Shop local!  Woot!"

But then it's not the friend's present to her mother, it's Perrotta's present to his friend's mother, and the friend has to find something else to give…  

That's why she wants to pay for it! That's the whole thing of this discussion.

Thanks for your opinion! ^^

i'd say it depends on your time. i too sell to a friend of mine a certain food, but i have to charge because i lose money. so, if you can spare some of your free time for her then i'd give it for free. but if it's time consuming and you don't need it for practice or something, then charge the amount you could've won by working for a stranger, possibly with a friend-discount that you specify.

i don't know any amount of money, it depends on how many hours it consumes. if i were in this position with little free time, and no need of practice composing i'd say 6-7$/hour.  it depends on the local economy too.

Write something great for free and they might pay you for a second piece...
Or you could ask for half a pizza. Because that was hilarious. :D