Safety razors are indeniably cheaper long term (although expect to pay $100 ish to get a good handle, brush, bowl, blades, and soap). You'll likely break even after ten years (assuming $1.50 cartridges Vs. 10c blades). You'll also likely receive a closer shave with a safety razor.
That being said... I did the whole safety razor thing. It was fun. But then I switched back to cartridges. Why? In order to get a good close shave with a safety razor while also minimizing the chance of nicks, cuts, and razor burn you need a good quality thick lather.
Unfortunately creating a good thick lather can easily take ten minutes. You cannot really use off the shelf shaving foam or gel because it doesn't provide enough protection for a safety razor.
So ultimately I decided I wanted shaving to be a 10 minute activity in the mornings, and not a 20 minute activity. Also creating lather isn't the most fun thing to do first thing after you wake up, in particular if you're working it hard (as you should).
Cartridges are quick and easy. They're the ultimate lazy man's solution. And you can use off the shelf non-foaming gels (e.g. "King of Shaves Alphagel", "Gillette Fusion ProGlide Clear Shave Gel") in the shower (and, yes, wet-shaves are a must either way, buy an inexpensive non-electrical anti-condensation travel mirror (i.e. you tip hot water into a compartment behind the mirror)).