If you want to compare prices you see with the cost of making your own shards, these are the costs if you were to buy shabby gems from merchant and take to jewelcraftsman to combine:
1 shabby = 530 coins
3 shabby = 1,590 coins will make 1 rough
3 rough (9 shabby) = 4,770 coins will make 1 blemished
3 blemished (27 shabby) = 14,310 coins will make 1 common
4 common (108 shabby) = 57,240 coins will make 1 average
4 average (432 shabby) = 228,960 coins will make 1 beautiful
4 beautiful (1728 shabby) = 915,840 coins will make 1 flawless
5 flawless (8640 shabby) = 4,579,200 coins will make 1 immaculate
5 immaculate (43,200 shabby) 22,896,000 coins will make 1 perfect
You can use this guide to compare to prices you see in catshops or in Auction House (AH)
(please correct me if you find any of these in error - thank you)