What would be the idea method to take? I've got 120m to use, I've seen players do it within 60-80m. Currently im doing (painfully) gold ore w/gauntlets to 80.

 

I wont grind it like a mad bat as I'll prob take breaks to work on dunge also since 100 dunge is another goal.

Addy plates are the way to go if you want to spend some coin, and get fast exp. At least that was accurate a month or 2 ago.

Runewiki Smithing Calculator

 

I'm not sure about mithril but addy+ is definitely faster exp then gold ore.

Another option of course is ceremonial swords. I' ve been doing them casually since they came out, using the coal from mtk mostly, and buying some here and there. I was level74 when I started too. It may not be the most efficient way, but wotj the ability to store 8k coal and 4k of each metal ore does cut down on banking.

you could consider superheating gold with gauntlets its around 80k smith and 75k magic xp per hour. You do loose abit but no more than any other method and you get mage xp too.

Grimy's Spreadsheets can help you with some of the calculations. https://spreadsheets.google.com/ccc?key=0AldEhLOK6ejJdEFqQjlybHhEQnZXQ3lZOU9icmJKSFE&hl=en#gid=0