Apple could not care less about that $99 fee. It is 100% immaterial to them beyond the function that it is attempting to server - act as a minimum bar of entry to the developer program.
Exactly my point - the $99 isn't a financial barrier, but, your average user isn't going to pay it each year, so it creates a minimum barrier between "Users" and "Developers" to provide Apple with some insight into how many developers they have.
Advance access to IOS kind of messed that up, (at lot of people paid the developer fee to access the next operating system) which is why application to the WWDC lottery is probably a better estimate of developer count.
It doesn't need to be a recent mac, I'm running Yosemite on a 9 year old Mac Pro. I think you can pick one up on eBay for under $400 if you look carefully.
