Wait a second, are we talking about margin or commissions?
Here's some extra data. I've bumped my starting capital up to $6,000,000. The initial margin for the equity symbol is set to 10.0. I placed a limit order for 65,104 shares with a limit price of $0.0256. The next day, in the simulation, the order was filled at my limit price. However, my current capital (SystemData.CurrentCapital) is now down to $5,348,960. ie, its down $651,040 when I've purchased shares worth a total of $1,666.66. Strangely my current equity (SystemData.CurrentEquity) says it is $651,040.
If I now change the initial capital setting for this symbol to 1.0 (instead of 10.0) then when I place the same trade my starting capital drops to $5,934,896 and my current equity is $65,064.
So my share portfolio seems to be valued at quantity * initial margin rather than quantity * share price.