For the standard awards, they used to use a fare basis of $0 but often the Gate Agents would manually override to $50 or $100 plus the bump compensation of $300

For a points based booking, it would be very easy to see what the cash-equivalent fare basis would be. (since the points multiplier you paid depends on the WGA/AT/BS designation you picked). each point used equals a set amount of $ (varying by fare type)