stormrage us, buying everything was around 4... leatherworking though... around 10 :/
On my server horde side there wasn't enough mats on the AH on horde side to lvl BS and eng. I had to get gold over to ally and buy the mats at a much cheaper price aswell
Roygbiv, 85 mage Khadgar
I did Engineering and blacksmithing at the same time, set me back around 35k. But old world ores are stupidly priced on my server. (thorium and fel iron cost about 5 times more per stack than ghost iron does)
I just recently done this on shadowsong server and it set me back 5k if that, seems pretty cheap atm. Good luck.
Leveling eng is the easy part. The hard part (if you want to call it hard) is getting all the cool toys created, a la Jeeves, MOLL-E, etc. No engineer is complete without those, imo. :P