don't expect the skipper to provide beer/snacks after the race. The skipper needs crew to race, so you helping is a good enough "race payment" in my opinion. Offer to bring a 6-pack or bottle of wine and some munchies. Also, bring your own lunch/food to eat during the race.
I know some skippers provide the boat and race fees throght the season, but expect folks to prep the boat in the spring and ready it for winter. However they have pretty steady crew.
I think it depends on the circumstances. It might be nice to offer to pay some of the fee or ask whether you can supply food and/or drinks, especially if it's just the two of you. When I crew in a regatta at my club, where we are co-equal skippers on the club's boats, my partner and I will split the cost. When I crew with someone who is paying $100 for 8 races during a series, I bring my own food/drink and the crew buys the skipper drinks after each race. If it's a one-off whole day race in which they're looking for crew, the skipper usually brings the sandwiches and I'll (sometimes) bring beer. I was on one boat in which everything was taken off at the end of the day and all the beer/sodas that we had brought were lugged back to the car. That wasn't fun....
The real answer probably is 'depends', as indicated by the responses above.
I've never asked crew to split regatta fees, but for much of our racing time we co-owned with partners, and all costs were shared - it also meant that we didn't need to line up many crew most days either, as the kids were usually along.
I think most skipper/owners who want to race are going to be happy to get reliable crew.. and anything the crew might bring to the picture is appreciated - but probably mostly the odd case of beer, munchies, and most importantly bottom scraping and boat maintenance and prep labour.
When race fees are onerous, such as the Vic Maui, then I think it's reasonable that the entire crew pitch in, if only to ensure they'll get the ride they want. On a commitment like that it's also a sign of genuine intent, with increased odds you won't bail at the last minute..
Also important that the crew and skipper/owner are more or less on the same page re dry vs wet during races, weight/gear restrictions, race schedule/frequency etc.
Like Faster suggests, if the crew chips in to pay fees, it's usually in a situation where they're pretty hefty, and it's arranged ahead of time as part of the deal, and everyone on the boat pays his or her share. (I can imagine how a teenager's share might be less than an adult's, for example.) If you really don't think a six of beer is sufficient, try getting better beer. You could also take a good look around when you're on board to see what sort of "boat present" might be nice. New sail ties? A fender? A fender cover? You could organize the crew and all chip in for new binoculars too. (hint, hint...)