A couple of weeks ago we discussed Schaffer's 'On What Grounds What'. Although we discussed quite a bit about different, non-equivalent ways of characterizing 'permissivism' in detail, I got the sense that there was a general sympathy towards the spirit of the contention that existential questions about numbers etc. were somehow easy, and the harder questions concerned what grounds what, and thus what is fundamental.
In particular, those in attendance did not object to the following constituting a proof of the existence of numbers (p. 357):
There are prime numbers.
Therefore there are numbers.
This is just an invitation to people not in attendance to share their views ;-).