Background
Sometimes I get asked what my belongings cost, be it an ordered food, PC, or other stuff. In the university I study, there is extreme contrast in how much students and their parents make annually between students. As a result, from time to time I get into awkward situation where the food is not expensive for me, but others try to claim the opposite. I might not call over anyone into my room, but since I live in a dormitory, I cannot pass by unnoticed by my familiars when ordering food, and deliverers cannot get right to the door of my room. I live with a person who doesn't care much about anything. The distance between fences where the deliverer waits for me (as they are not allowed to get in) is quite long, so meeting someone I know is guaranteed and ordering food considered quite expensive in the dorms.
I live in middle Asia. I'm concerned with their thoughts because they might start generating attention to me, which is of very big concern to me. I live a life between my room and university, spending time on research and other stuff. Getting more attention usually means spending time on dealing with others.
Question
How do I deflect or avoid questions like "How much does it cost"?
Example
I'm going to my room with a package of food.
Familiar: Hey!
Some entry talk
Familiar: That food smells delicious! How much does it cost?
I make up something depending on the person asking // *
Familiar: Oh, that's expensive! //I made incorrect guess
What should I tell on the line marked with '*'? I can keep making up numbers, but I'm sure one day they'll figure out I'm not being honest.
What I've tried
rucksack
My best bet is carrying a rucksack with me. Unfortunately, sometimes I order a pizza, sometimes deliverer gets soup spilled all over package, so it is not always an option.
headphones
I may pretend that I don't hear them, but pretending that I don't see them would be blunt lie.