I think you should say 15k-20k. If they shoot you down try 12k-15k. Do not go beneath 5k. You're incredibly talented and you deserve a lot more than You think for this dress. Besides, if you're goIng to go to college, having a larger sum of money available will be absolute Heaven for you, trust me.
I agree do not go lower than 5k as it is one of a kind and you did spend 100+ hours. Look at what couture dresses go for in Paris or London.