In Dental discount the payment is usually upfront. That is you know how much you have to pay for your dental treatment when you go for it. (The amount you pay in brackets)
Root Canal Treatment - Front Tooth $542 ($336)
Root Canal Treatment - Bicuspid $646 ($403)
Root Canal Treatment - Molar $829 ($491)
If money is tight what you can do is visit the dentists around your area and get an estimate for the overall dental treatment for whatever dental problem you have. You could outline your position to them and ask them to give you an overall plan so you can plan your treatment over the course of a year or two and also negotiate a discount. If you already have a dental discount card chances are that the dentist may not discount his fees any further. But you can still try.