I'd sure charge more than $20. You got to figure that even buying bulk you are going to pay 8.00 lb. for crab legs of the King Variety. You can probably get boneless ribeyes for $5.50 per lb. (Choice). So you are talking a leg (king) of let's just say 1/2 lb. $4, plus a sixteen ounce steak = $9.50 x 3 (too make profit) = $28.50 per. With side dishes, bread and incidentals increase $4.00.
Feel free to look at my website, It is priced out using the 33% rule.
My math dictates 33% food and supplies; 33% labor and 33% profit. Yes, it fluctuates north and south, but that is my target.