Rocks to start in 220 grit??

Your choices are pretty much between plastic beads and ceramics with plastic beads. I personally feel that plastic beads are a necessity from 120/220 on (and often times even in course) as it helps with fracturing that tends to occur in the microcrystalline quartz type rocks. I tend to add about 1TB per lb of rocks, or enough to fill to 2/3 a barrel, depending on what's more appropriate. With pellets, you only want to reuse them in the stage they were previously used in or after. So for example, you wouldn't ever want to use plastic beds in pre-polish that were used in a 120/220 stage - you would only want to reuse 120/220 pellets in 120/220 or course stage.

I'm fairly recently a convert to the ceramics and I do have to say that I'm liking their function in the tumbler. They take up a fair amount of bulk, fulfill your small "rock" quotas (which can be difficult sometimes) and are reusable in any stage. Not to mention, they last a long time and did I mention you can just clean them real well and use them where ever you desire? Even with that said, I don't think they can entirely replace beads - the beads work very well for cushioning the rocks and preventing late stage fractures. But, however, they can significantly reduce your need for pellets - especially in the latter stages where you don't always have a good supply of rocks and using new pellets every time is advised to prevent any chance of cross contamination.

In lieu of pellets, you can also use things like plastic BB's or other small, plastic based materials. The pellets can be found at the rock stores or even your local craft supply place, where they're sold to stuff pillows/animals/creepy dolls. The good pellets will float, making it easier to separate them from your rocks.

Anyhow, that's my 2 cents. Hope that helps!

I'd agree with John as well, saving up to 2/3ish is the best plan in order to get the most from your materials. You'll be surprised with how much material 120/220 alone takes off. From pre-polish on, you don't lose nearly as much. You still want to use pellets though, even if you have a full load.

With a 2/3 full 120/220 batch for a week or two, I usually get right about where I want to be with the latter stages of pre-polish and polish. I try to aim for approximately 2/3 rocks and 1/3 pellets in the final stages. (Out of the total 2/3 recommended fill level) This insures you have sufficient cushioning and I've also found helps with the latter polish stages on some types of rocks.