Tl;dr Demo skis are a great option if you don't get that many great days.
Since I don't get enough pow days, I use demo skis when there's pow! Last season I had 2 powder days (in revy $$$) where I payed $30 per day for big fat k2's that were insanely fun. If you don't use them that much a season, I think demos from a good shop (not the mountain rental place) are at least worth considering. The only actual downside is that the bindings are heavier, and I guess having to pick up/ drop off (but a lot of the time they make it super fast and convenient). Obviously not a good option if you use pow skis more than like 4 or 5 times a season.
On a sidenote... Remember that you DONT need pow skis to enjoy a pow day. If you actually have some decent technique, skinny skis can shred. Think back to skiers from like 20-50 years ago.