about how much would it cost me to powerlvl engeneering from 1-350?

depends, are you also a miner? or are you planning on buying all the mats in AH?
Also, your race would be a factor (my gnome's racial +engineering bonus saved me some gold).

Depends entirely on your sever Auction House. That is if you choose to not mine. Cost my friend around 2000 gold 0-361. I do recommend the mining though, good cash cow at 70, kinda a pain to level though, your call. But it won't really hit until after 300 where you need abundance of Fel Iron to level.

well, at lvl 59, i switched from 310 LW and 323 skinning to mining/ eng. it took me a week and maybe 20g to get it to 300, thats farming mats and crap too, and i didnt get a epic mount until 64.