Basically, if it ain't free it ain't happening and then you'll be stuck with NAS without ADSB below (say) 10,000'. That would not (in my view) be a good end solution.
Therefore: You now think that NAS is not a good solution.
ADS-B and NAS are not interdependant - the timelines are separate - NAS in a few weeks - ADS-B a few years.
On A a separate line -- How does ADS-B work with overseas based aircraft? Obviously no overseas aircraft is going to have one fitted, therefore SSR still required, so where are the costs savings on Radar?