I understand your boss. Doing that process manually costs him X$/yea., Having you develop an automated solution would cost Y$ + Z$/year for maintenance/changes/bugfixing. Y / (X – Z) is the number of years before your former boss would break even. If X is small enough then it might simply not be worth the risk of automating it.
So lets assume you do it for free. You’ll still have to figure out these numbers. How much is Y that you’re giving away. How much effort is it going to be to maintain the tool, adapt it to changes? Will do that for free as well? For how long? Or would he pay for that? How soon would these changes be necessary? The whole exercise will do nothing for you or your former boss if you build this tool for free and he can only use it once or twice because of some changes that neither is willing to pay for.
If you feel the above numbers would be favorable you could investigate the possibility of getting your former boss to outsource this work to you. He pays your company a little less than what it costs him to do it internally and you are free to accomplish the work however you see fit. That way you take the risk he or his boss isn’t willing to.
Or it might be better to just prod your network for actual paying jobs. They – presumably – were happy with your work before. So instead of fighting over scraps that may or may not be worth doing, capitalize on your good reputation with them to get a foot in at a bigger project. May not happen immediately but would most likely be a better use of your time.