Engineering question: Firework and the priceFollow

Okay so here is my tale and question

Some few days ago i was hanging around in Ironforge and was bored...so i thought to myself, what could i do make things a little more funny..Then it came...I had the schematics from lunar festival but hadnt used any of those fireworks yet. So i began to get the mats for it and make the 2 diffrent launchers and about 180 rockets/clusters. Before i was going to blow up Ironforge i did go to the bank and see if i had anything else...Lots of diffrent event stuff(like raining roses and moonlight)...After been makeing my preparation i saw 2 female night elfs(hey im a guy, can you blame me) that was danceing...Kaboom it said and the firework startet. More people cameing and startede danceing, drinking and other things. After the little show i made, i logged out. Later that evening one of the 2 nightelf /w to me and said thx for the show....her friend(the other night elf) was in a sad mood until i came and made that firework show and she asked me if i wanted to make some of that firework so she could do it for her friend.

So my question is now...how much should i charge her for it?
1: Its engineer stuff that DOES NOT require engineering
2: Its event stuff
3: the diffrent mats are stil exspensive.

Many thx for your input on this subject, this little rogue gives his thx and blows up big cities.