I have read some managed to put ROCK on a NUC which is not on that list and were successful. Roon say they do not guarantee it will work and take no responsibility (which is fair play).
I ordered a NUC8i3BEH this week from a Spanish website www.techinn.com and they had very good prices compared to what I had available in the UK.
As @ged_hickman1 suggested, eBay is also a great place to find good deals.
EDIT: Just seen the site I ordered it from offer to split your payment over three months with Klarna or Paypal. This may help with your finances.