'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Sure it's possible. You will need the crank, possibly a new bottom bracket (depending on what type of crank you now have and what replacement choose) and likely a new triple front derailleur. Also depending on the model of your shifters, you may need to change the left (front) shifter for a triple compatible version. Your rear derailleur may need to be changed or you will have to live with its limitations.
So, it could be a cheap as just a new crank and fd or quite expensive if you need to change the bottom bracket, rear derailleur and brifter also.