Currently @ level 30 Blacksmithing, and most of the synths at this level range involve using a steel ingot or sheet. Considering I've only ever had one HQ synth for steel ingot from Iron Ores this is proving to be an expensive area of levelling Smithing as I have to buy from AH. Stack of Steel Ingots currently going for 40 - 43k a stack on Remora.
Don't buy them from NPC's in Mhaura, the rip-off merchants are selling ONE ingot for over 19k!