the only wide rims (especially in 18, 19 inch+ sizes) are always expensive new, and the nice ones are usually pricey second hand too (if they even stay on the market for that long)
all the crappy Chinese or Taiwanese 'Vork Racing' by 'RAVS Engineering' and similar wheels are made in smaller sizes with pathetic widths (6", 6.5", maybe 7" if ur lucky) to suit FWD cars, and have huge offsets too
look at Commodores- even when they had 245mm tyres, the factory was still fitting them to narrow rims- hence when you look at aftermarket rims for them in 18" sizes, they are still fairly narrow
If you want anything over 9" wide and quality, to suit a Skyline, be prepared to spend some meaningful cash