TL;DR: IMO, all goals should always start at $0 with free short circuit to $5; we should have 1 permanent freebie; it would be great to have a $1 pledge amount for Beemium subscribers (which we could skip over on most goals since we have free short-circuiting).
IMO, All goals should always start at $0 by default and move up from there when they first derail. (With the first short-circuit from $0 to $5 being available even to non-premium.) We're just never really sure what we can really do, realistically, when we first start a goal, I think.
I also think each user should have at least one perma-freebie at any given time. E.g. you could step a goal down from $5 to $0 only if you had no others that are permanently free or stepped back down to $0 at that time (and none in the process of being stepped down to $0). I think there is good reason to want to Beemind something like weight, for example, without having it cost, since people are likely also minding other related goals. (Just-created, never pledged goals shouldn't count towards your perma-freebie limit.) I use permanent-freebies for test goals and for only two other goals. I'd be fine with giving them up for the test goals, as well as with giving up permanent freebies on all but 1 of my goals (and I am minding something like 70 goals). Sometimes I like to reward myself for a long time without a derail by stepping back to $0 to see how I do without the sting (hint: never well) but I'd be fine with giving that up.
I wouldn't mind having a handful of goals that could be $1 goals, too, though. But I think that should be a Beemium feature. Use case: I mind each weight training exercise separately. I really don't want to pay $80 for missing a workout (16 exercises x $5), but would be perfectly fine with paying $16 for missing a workout and derailing those 16 graphs.