The pen (wand) type bar code scanners work best for tabulations.  These connect to the USB port of the computer.  

Scanners are available from $85-150.  We have had good luck with the Unitech scanners or WASP scanners (below).  These are available from PC Connection and CDW for under a $100. 

Any pen type scanner that can read and decode Code 39 should work.

Notes on using scanners:

When using a USB to PS/2 adapter the bar code may not reading properly (missing characters).  This may corrected by setting the inter-character delay,  Use the shortest value that allows the reader to work properly (ex. 3 ms).  This appears the caused by transmitting the code to fast.  The delay causes a pause between characters.  NOTE:  ALL USB to PS/2 adapters are not the same.  Some work and some don't with scanners.  TEST prior to the contest.