I've never actually had any 'Princess', frustratingly, so I can't comment on its sturdiness - but most Holmegaard stemware was designed to be used. I've had a suite of 'Canada' for a few years now with no casualties.
Technically they shouldn't be terribly expensive, as they were in constant production from 1957-1995, passing from Kastrup to Kastrup-Holmegaard, and then to just Holmegaard, but they still do seem to fetch fairly sizeable amounts on eBay, with the more common sizes going for between £60-80 per set, and the scarcer ones, such as the champagne flute, going for anything up to £30 per glass.