There is no hard and fast rule about how much a program charges for an elective as a medical student.
Some places, Harvard and Stanford come to mind, charge the equivalent of 1 month's tuition...this can be upwards of $3,000 USD. Many, many places charge nothing. Some may charge a couple of hundred dollars...it really varies.
IMHO, foreign students make the mistake that it only "counts" if they do an elective clerkship at some internationally known institution. Perhaps, but consider the fact that these places are rife with clerks and you might find it more difficult to get the attention you need to get a great LOR. Besides, if you have financial difficulties it seems a bit ridiculous to spend $3000.
I am unaware of any waivers for foreign students.
Here is what you need to do:
1) choose an area of the country or some particular institutions you are interested in doing a clerkship at
2) go to their website for the medical school and look for information on Visiting Clerkships/International Electives (or something like that)
3) follow the application instructions. Most places are very detailed oriented...you must complete the application as it states, otherwise you will not be considered.
I think most places will not consider you without USMLE Step 1 - they have to have some assurance that you have at least the basic knowledge they require of all of their own clerks. In addition, as I noted, you will have to have health insurance which will cover you in the US; sometimes you can purchase that with your plane ticket.