a bag will last a VERY long time for field points...if you get one that has replacable covers, you can replace the covers periodically and it'll last forever....the insides of them really dont deteriorate at all..
for broadheads...good luck. broadheads cut...theres just really nothing that will really do GOOD with broadheads...i like the cheap 20-30$ hard foam targets that are like 2-3" thick...life is decent...and price isnt bad...and instead of pulling the head back out backwards, you can unscrew it...that makes it easier than pulling a head out backwards...and you save a little wear off your target....then when you got one wore out pretty good buy another and glue it to the new one...i used the clear wrap made for securing items before you move...like plastic food wrap but it stretches and holds pretty well...it worked and with the 2 combined the life has been decent..i used the plastic wrap so i can undo it and rotate them each different ways so i can shoot different spots...works for me...