Assuming this guys are all dev. at $4000 month (easy premise!). I would say $1,500 + $12,000 + $12,000 + $1,500 (let's say it's modules are equal to the hull) + $10,000 (arbitrary for buying protection)
$37,000? That's crazy! :)
If you're going to go your route it would be best to just add 20% of the purchase price on and buy a character and another 10% premium on to buy one off the market.
If you look at the cost of labor involved involved (assuming real world wages for the time spent) in building a Titan the cost would be absolutely massive, even discounting the huge infrastructure requirements.
Of course, as I believe someone else pointed out, you (or your alliance more like) need to guard the construction site while the Titan is being built -- so the cost of building one of these is definitely huge. I guess $1500 is a bargain, all things considered?
The hard part of that is the infrastructure - you need to own a star system and put up a bunch of towers and fuel them and haul/build/mine the components and minerals to your (hopefully out-of-the-way) system, and you need to have firepower on call to defend your operation if you're attacked. And the character training to pilot the Titan needs implants that are expensive and mean he can't be risked in combat (so you need a second account). Most of that (owning star systems, on-call firepower, maintaining towers, hauling/mining minerals, having spare/secondary accounts) is stuff that large alliances have to do anyhow for their other strategic needs (equipping sub-capital players, paying bills, constructing jump bridge networks, etc.) so for them it's just a bit of extra load on the logistics team, and they usually have economies of scale (they have so much money and space they can have 3 Titans in the hopper at once).