Agreed, the lower steem is valued the more it will be burned. We want communities to be attractive enough that it would create a good burn rate for steem. $0.40 or 3 steem would be way too low. If it's fixed to a specific dollar value and steem goes up in value, all you have to do is hold on to your steem till you can afford a community. Any name 5-6 characters or under should be sold at a premium price. Like if you tried to register "zap" you would pay 10,000-20,000 steem or something.
For non-premium names maybe $25-50 worth of steem.