I've fairly recently invested in Heliopan 100x100mm filters - and I think the key word is invested! They don't come cheap which is the only drawback apart from being breakable. That being said, I'm delighted with them and I wouldn't trade them for anything else.
The website has a pricelist PDF which is probably still current (2006 stock at 2004 prices and includes vat).
However, it isn't only the glass which is expensive but the filter holder and any step up/down rings if they aren't already compatible with your current system. Here's a rough calculation, all prices are per piece (100x100mm) and it would surprise me if the competitors weren't about the same:
Professional filter holder 200eur
Filters price group 1a 144eur
Filters price group 2 170eur
Filters price group 3 200eur
Linear polariser 245eur
step up/down rings 45eur
That's mighty expensive glass and as far as being able to see any visible difference - I very much doubt if anyone (now there's a challenge) could tell the difference between images with resin Vs glass filters.
For me, it was both a bit of luck and long term convenience. I picked up the holder and deep red filter for 40eur and it's now pretty much compatible with all of my LF and MF lenses. Previous to the lucky find, I was looking into the Lee system and I'm sure that I would have been just as delighted with that.
To be honest, I think it would probably be far better to put your "hard earned" cash elsewhere unless you've got a tree growing out back...
And as a final word, let's face it - when your photography comes down to the decision between glass or resin filters it's a luxury problem.
Goodluck with your decision - I'm sure it will be right no matter what