Cost isn't the only variable when deciding the most suitable security credential, however, it is an important factor.  There is a short, but vague, answer to this "economical" question.  It depends on the number of credentials required.

Latitude provides a quality, name brand proximity reader for about $125.00.  This reader needs to be coupled with Proximity Cards, which range from about $3.00 to $5.25 each, depending on form factor, colors, and logo.  

Barcode readers come in two primary form factors:  A swipe reader is when the user has to guide the card through a slot where the laser reads the barcode.  This option is about $475.00.  An optical reader reads a card that is presented in front of a sensor.  Optical readers are more expensive because they can read different types of barcodes, QR codes and phone screens.  The reader that Latitude offers is about $900.00.  Barcoded cards are about 3x less expensive than proximity cards with prices ranging from $1.50 to $0.50.  

At what scale of users does it make sense to consider barcodes over proximity cards?  The magic number is around 250 users.  

Here is the math using the assumptions above, plus volume pricing for credentials: