When you say you don't pump anymore, do you mean he is no longer breastfed? If he is exclusively breasfed, you should be using a vitamin drop supplement (Poly-vi-sol is the one we used, I think). Check with your pediatrician. If he's getting that, he's getting plenty of iron. If you're not breastfeeding any longer (sorry for my confusion), then he should be on some kind of formula, which also has plenty of iron.
Either way, he shouldn't be needing the cereal for iron. The cereal is to get him used to eating solids.
Also, if you're still breastfeeding and you have a pump, you should use it to pump some milk to put in with the cereal - just pump a little and you can keep it in the fridge for several days. Or, pump a whole bottle and freeze it in a covered ice cube tray, then move to a freezer ziploc. Then you can just thaw a cube every day to mix in with his cereal. You can also mix up some formula to add to his cereal as well - the idea is the gradual taste difference of milk/formula + cereal, while you change the ratio. Remember, the cereal is new to him as is the fruit (which may be too sweet for his tastes, try sweet potatoes instead), the sweetness of the milk/formula is what he's used to.
I'm about to start my 5 month old (today) DD on cereal this week, hopefully it will go as smoothly as it did for my now 4-yr old.
Good luck!