Could you please explain the difference between a 3/4 crown and a veneer when it comes to a peg laterals? Price difference?

There isn't much to explain. They are the same thing, Material is the same, the time spent is the same, so the fee is the same. 

The difference between a porcelain veneer and a ¾ crown is mostly a technical issue. With a peg lateral or other undersized tooth we frequently need to fill the space on the inside of the tooth to avoid unnatural contours   and gaps that would be created by a veneer on the front of the tooth. Once you wrap the ceramic onto the palatal side to do this it becomes a ¾ crown. The cost should be the same.

The only difference between an actual veneer and a 3/4 crown is where the dentist feels the margin needs to be on the inside of the teeth based on many variables. Your dentist will use their clinical judgement to decide and thats the really the only difference between a veneer and a 3/4 crown.