I still think you're right, Dave, but just wanted to add a little more detail. It likely will be a bit cheaper with RGB. You'd end to put a parts list together to know for sure, as there's lots of price difference in all the various controllers. For me, it was a choice between the two looks. Having the multiple strands of LEDs creates some extra "movement" that you don't get with a single set of RGBs. However, with the LEDs, you're limited to the three colors you choose instead of the limitless palette of color with the RGBs. I chose the "movement" over the millions of colors.
For completeness, consider this: Bob talks about 8 trees of 3 colors, so that's 24 strands of lights and 24 channels. So, the equation should include 24 strands of lights, enough controllers to provide 24 AC channels, enclosures, and whatever is needed to plug the lights in (zip cord, plugs, outlets, whatever your setup uses).
For RGB, he needs the lights - 8 strings of RGB. He also needs to control them. So, depending on the protocol he needs, he would either need 24 channels of DMX from a DMX dongle on his PC, or 24 channels of DMX from a port on his pixel controller, or 24 channels of DMX from a protocol bridge. Or a DC controller with 24 channels. Also, power supplies are necessary for this approach. So, there are a few more things he'd need to buy.