Here's another thing about academic conferences. Even if you're fortunate enough to be employed by an academic institution that will cover some of the costs, often you're expected to cover some costs and be reimbursed. Hotel costs are the most common, since hotels really only want to deal with credit cards, and academic institutions are reluctant to cut a check in advance for the cost of the hotel (plus they'd have to know exact cost including tip, etc). I'm able to do this, but I know a coworker has had to discuss her financial situation with our (understanding) boss in order to make conference travel possible for her. Not everybody has a credit card or room on a card for this kind of thing.
Local open source tech conferences I attend seem to be pretty good about getting sponsors. They get space at a university, which also sponsors other things like catering sometimes. $25 for a one day conference is pretty common. And you can volunteer for a free/reduced membership.
Major academic IT conferences in my area of expertise (EDUCAUSE, for instance) can easily run $600-$700 for registration, plus hotel, meals, etc. The registration fee is often waived if you're a presenter, though, so that's one way to make the cost a bit more manageable for institution or self.
Professional certifications aren't quite the same thing, but I've definitely noticed since getting my project management cert how expensive continuing education (I have to do a certain number of hours) is; a lot of these opportunities assume I work for a corporation that will pay for super expensive conferences or other things. I could go on a fucking cruise and collect a zillion Professional Development Units. What. Thankfully there are options that are free (reading related books, if I can get the books) or free with my membership to PMI (which is also $$).