Slight Translation Error

I was walking through Plaza de Independencia with my friend from Baylor, Landree. They have street vendors set up for tourists and locals to buy fun things so we were walking around looking at all the trendy things to bring back to the States with us.  One of vendors we met was very friendly and knew enough English that we could have a decent conversation with him.  I asked him in English how much something was and he taught me in Spanish that to ask that you say, "¿Cuantos questa?" I practiced and practiced until I rememberd well enough to move onto the next vendor and ask her the same thing.  I walked up to the woman, found something pretty and said, "¿Cuanto questas?" Not much of a difference, right? I only added an `s` to the word questa.  She corrected me very quickly and told me I should not say questas, but questA. I thought, no biggie, I make mistakes like that all the time when I'm practing my español.  So I go home and tell my brother everything about my day and mention how awkward it is to be corrected in your Spanish.  He then informed me that I had asked the lady not how much her item was, but how much she was.  Needless to say, I have learned my lesson, and I will not be adding an `s` to the word questa.