Nios was part of the IP that came with my Quartus subscription last year.
If you want to add Nios to a free web license I think that is $499
That seems to be what you also get with a Nios kit. IIRC the Nios subscription never runs out but only works with Nios updates up to 1 year from the Nios kit or Nios license purchase. IOW you can keep using the original Nios and
some later updates forever but after a year newer versions will not compile without timeout.
This is all consistent with 3 yrs Nios experience but may be inaccurate in some detail.