OCD will give you totals or at least mine will. First, select your entire collection in table view (or whatever albums you have entered values for). Then highlight (select) the ones you want the total for. The amount will appear in the bar at the bottom of OCD along with number present and number selected. Be forewarned that box sets add the amount for each album. I.E., if you paid $25 for a three CD set, it will value each album in the set at $25 or a total of $75. So if you can find a way around this (you could divide the cost by number of albums in the set and enter that I suppose), you will not have an accurate total.
The bar will also give other totals such as time, etc.