How do you respond to people who ask how much you bought something ?

That depends on who is asking. If it is the recipient I tell them don't worry about it. Or inform them that it's rude to ask. If it's someone else then I might ask them why they want to know or just tell them as there is no harm in someone knowing how much I spent on someone else. 

REspond: "Why do you ask that question?"

That depends on how well you know them.

You could just laugh and say, “Too much!”

I never get that question but i hardly ever go out but if someone did ask me that i would just not respond or pretend i didn't hear them. Nosy people are always looking to start drama and there's no reason to add any fuel to the fire they're looking to start.

They are busybodies. Refuse to answer. 

Mia it is none of there business

Eh.

I only think it is stigmatic for certain things - mainly like a house although weirdly enough I think with enough Google search one can discover the going value (and sales history) of just about anything these days.

I am generally vague with most questions or any type - so in the case of how much something costed I'm either proud to say how much I spent or I'll just say "Man... it was a lot..." and if they know me at all they'll be able to pretty-much envision a number on their own.

I don’t have a problem telling price but I HATE coworkers or anyone touching my clothes while asking me questions like this. I have problem with anyone touching me or touching my things. Keep your dirty hands to yourself. 

Tell them honestly how you feel about it might hurt them a little but you feel its rude to ask someone that. 

I would tell them to mind their own business