Are small conference posters bad etiquette? I am displaying a poster at a conference. The board is 4 feet wide and 8 feet tall. My university offers 1 free small poster print per semester. I used their service and my final poster is only 3 feet wide and 2 feet tall. 

The conference had no specific sizing requirements on their website. I contacted the conference organizers and they said it's small, but OK. This is my first conference. I still have time to pay a private printer for a larger size, but don't want to spend money if I don't have to. Is it bad etiquette to have an undersized poster?
A 2' tall poster is too small. I would not recommend a poster smaller than A0 size (about 3' x 4') nor larger than 2A0 (4'x6'). For a 4'x8' portrait orientated poster board I would recommend not less than 3' wide, but would not go all the way to 4' since often the boards are displayed in an accordion style resulting in lost width. As for height I would go no more than 5' high. While you do not need to be able to easily reach the title, no one likes reading at their knees. In other words, A0 size would be slightly small, but okay.

Depending on the material, I would suggest looking at large format black and white printing. For example, staples will do a 3'x4' black and white engineering print for $7.29.