The IETF is completely open to newcomers.
Some good news for your travel budget: it's possible to participate in the IETF without ever attending a meeting. If you really want to get results, you probably need to attend some meetings, but it's certainly not required to get started. The IETF carries out most of its detailed technical work online, with the primary method being email.
Every IETF Working Group has a dedicated mailing list, and that's where proposals are made and discussed, where issues are raised, and where consensus is established. (Since the IETF has no formal membership, decisions cannot be taken by voting; the method is to establish rough consensus on the mailing list.)
After participating by email for a while, it may be time to attend your first meeting. Details are linked off the IETF home page as soon as they are available. This isn't free; apart from travel and hotel costs, there is a meeting fee. Be sure to arrive in time for the Newcomers Tutorial, always held early on the Sunday afternoon before the meeting starts. It will give you a lot more information than this brief introduction.Â
Also on Sunday afternoons, typically between 1600-1700 local time, is the Newcomer's Meet & Greet, which is a hosted reception where first-time attendees and WG Chairs mingle informally for an hour. Try to stay at the meeting for the entire week, so that you can sample other WGs as well as the ones you have been following in detail. And make a point of speaking to people around you, during the breaks and mealtimes. There are usually at least 1000 interesting people at each IETF meeting.
Every experienced IETF attendee was once a newcomer.