OK this prank is not only cheap but it is very simple to make. My friend is in the military and when he came back home for a few weeks we decided to prank him. its only fair since we always try to out prank each other.
so this is what you need:

2 quarts of mint chocolate ice cream (about 1.97 at wall-mart )
1 pack of wasabi (about 1.50 at wall-mart)
1 bowl
1 spoon

Step 1: Mixing

The reason for two quarts of ice cream is so you can eat yours(witch is safe). and your friend can have the pranked one!
Take half of the ice cream out of the quart using the spoon and put it into the bowl. take the wasabi and mix all of it in the bowl as well. then mix them together with the spoon, mix thoroughly since it is still frozen. (it will get easer as its mixed).
When mixed add it back into the quart with the other half of ice cream and refreeze. (you only mix half of the ice cream to make the wasabi more effective even though a little goes a long way.
they sell a tube of wasabi at wall-mart that is the perfect size and cheep! (remember a little goes a long way!

Step 2: The Setup

Invite the person you want to prank over to hangout or to do a movie night.(whatever you do)
when over just walk to the kitchen grab your ice cream and his. usually i mark mine on the lid so i don't get confused. and hand it out.
the second he takes a bite he will be running for the sink. i wish i had a video of my friend doing this but i found one video on youtube.

www.youtube.com/watch

They say its green tea ice cream, but its more practical to hide it in mint chocolate chip ice cream.