But you can totally walk into EVE, drop down enough real money to buy gametime coupons that you can sell for enough ingame money to buy a character (on the offical forums) that can fly a titan and then buy an existing titan. You don't have to bootstrap your way to your spaceship with a pickaxe and a roll of duct tape.
So how much would it cost to actually buy a fully functioning and outfitted titan? Assuming your character can already fly it, you have the personal know-how to use it, and that all other practical considerations are separate.
In actual practice, no single player will construct all the components for a titan. An alliance will spread the work of building the components around, especially since some of the same components used in titans are used in other capital ships and can be allocated to building whatever is necessary.