Welcome Big John.
I have looked at the Sharebuilder offering in the past, and it does have some attractive features.
But for me, with relatively small amounts to be invested, the numbers didn't work out. It was not "low cost" in comparison to mutual funds or ETF's.
Between the monthly charge and the $75 back end fee to close an account, I figured $150 / year. That's 1% annually on a $15,000 account. If I had prospects of a 6-figure account balance in the near term, my view would be different.