I am currently prospecting for a new round of UX design projects. The prospects are all in the same industry. Some are local, others non-local but domestic (US), others international. Prospects from at least 4 continents are on my list of people to contact. Travel costs to see some of them could easily run US $2000-3000+, and more if the travel is urgent.
While I'm open to doing some on-site travel, my concern is that prospects will want me to go on-site before I land the project. If they aren't my clients yet, they haven't signed any sort of proposal or contract yet saying that, among other things, they will pay for my costs of travel and pay for my work time while on-site. (Assume that while I'm on travel, I won't be able to work for any other clients until I get back, so my paycheck is $0 if I'm not paid back.)
How do freelancers commonly handle this situation? Is there a generally accepted way to approach this?