get RSS feed notifications on ios and mac?

The good news is that it is possible to do what you want by using the IFTTT service.
This is a service that can be used to take a number of actions in response to a wide number of triggers. It stands for "if this then that ".
One of the triggers allows you to specify an RSS feed, and one of the actions is to generate an iOS notification.
Rather than explain it fully here, I'd suggest you Google the query "iPhone notification from an RSS feed using IFTTT ". There will be many results which will help you.
One other advantage of setting up a free IFTTT account is that you can then use other triggers to generate notifications. For example, if a specific twitter ID sends a tweet with a specified keyword then you can get a notification. I use it to get alerts from the twitter account of a train company that mentions my local station. You can also get alerts when the weather reaches a specified temperature. In fact there are hundreds of triggers and hundreds of actions, so once you start you can really make good use of this service to get some very personal, targeted alerts

I find it interesting that a solution which meets your requirements exactly and provides the opportunity for many additional notifications and uses, for $1.99 per month, is unacceptable on an iPhone which probably cost over $800. Developers and service providers have bills to pay. Just a shame you see it this way