I've been using tetanal c-41 press kit from B&H for ~$20 and have had good results for about 20 rolls, and I've let the developer sit for around 4 months at a time before throwing it out. I'm happy with the $1.00 per roll (including 120), especially now that the local CVS stopped developing film in house. Now it takes them a week to develop for $5. I may try another form though, like the Rollei/Compard Digibase C-41 Midi Color Processing Kit from Freestyle to see how that goes. I'm new to this, so I'm still testing out different methods.