Four mana is the minimum for a simple clone. If nine can give five tokens, three tokens won't be far behind. In my opinion, a three token copy would cost at least six (and at that, a 3 token copy would be awesome). Ultimately, I'd place the value all the way up at seven or eight, right next to the original card. Copies en masse are potent as proven by rite's playability.

If it's going to be in the same Standard or the same block as a batch of creatures with ETB effects, then it basically has to be pricey because of the geometric-growth issue. So it can't actually be that much cheaper than Rite. I think that they were rite to make the kicked version of Rite splashy. At three copies, it's interesting, but not as appealing as a Johnny/Timmy card. At five copies, we start to get big juicy effects worth building a deck around - like the Allies.

Your question is also an isomorph of "how much should Rite of Replication cost with multikicker," which is the other interesting way to design it. Because it's a Clone, again it can't really cost less than 4 - and 2 clones for 3UU is clearly overpowered (if two 4/4 dragons for 6 is good, than two anythings - say, two BSAs - for 5 is way too good). So you're looking at a multikicker cost of at least 2 or 3 - which is less efficient than R of R is presently!

Rite of Replication is definitely a carefully designed card with a lot of moving parts. It works the way it does for a reason.