I didn't do alchemy but I did do engineering by buying all the mats. Yes, I payed for the very expensive old world bars rather than farm them. Once you get to 80 make a ton of gold doing dailies with the goal in mind that you are going to be buying mats. I am not sure of the difference in time but if you think farming is a waste of time then do dailies/heroics or find some other means to get the mats.