Firstly sounds like he wants to see his son... which is a good thing, (in 99.9% of cases)and it will benefit your ds to have a relationship with his dad.
This is not about what is easy for, who it suits, or anyone holding onto adult relationships. It's about your ds and his needs etc.
so..having said that ( felt I had to because sometimes it gets lost).
I actually feel really sorry for the dads out there who used to see their dc's everyday and then are cut down to every other saturday.. and it's crap for the dc's too. I mean if they live near enough what is wrong with them seeing the dc's after school etc.
would it be an option to e-mail each other regarding changes in arrangements.. because this way you can't actually argue.
Where money is concerned if the standing order doesn't materialise.. go to the CSA. ( they aren't always great.. but that's the option.)
My ex has the ds's every other friday afternoon to sunday evening plus half of school hols, and for anything special.. or if he can get down to see them. ( he lives 200+ miles away. We do money through CSA because it saves arguements about money. And he used to pay double.. and this now allows him to do nice things with his sons etc. ( because why shouldn't he).
what I'm trying to say is.. this is your sons relationship with his dad, no longer is it your relationship with your ex. might be worth looking at it in the light that you are actually helping your son, does it really matter if his dad wants to see him or pick him up from school.
maybe you both could sit and set up a better contact agreement for both of you.