With R09 one-shot at 1:50 doing two rolls at a time, and Ilford Rapid Fixer at 1:4 lasting for five rolls, I reckon it costs me about £0.60/$0.90 per film in chemical costs, which is much better than the £5/$8 I was paying per roll for BW development. If you use a simple changing bag and Paterson two reel system you can probably recoup your equipment costs and start saving money fairly fast.
Then you can spend that money on lenses
Also, being able to get a quick turnaround on your films is great, plus the ability to experiment and get different results depending on developer/time/agitation. If you print or scan too, it's very satisfying having completed the whole process from the first click of the shutter yourself.