Be a steal
Definition 1 of 1
Pro Tip 1/3Colloquial Use
The phrase 'be a steal' is commonly used in casual conversation rather than formal writing. 
Check out these shoes! They were a steal at the weekend market.
Pro Tip 2/3Positive Surprise
This phrase often expresses pleasant surprise about the low cost of something valuable. 
This vintage jacket was a steal at just $30.
Pro Tip 3/3Implication of Rarity
'Be a steal' implies that the deal is unusually good and might not be found again easily. 
50% off on this designer dress! It's a steal and won't last long.