Since so many apply to medical school and so few get places, the first place you need to look is at your scores, as these are the first filter your application goes through before anyone looks at it. Your first move is to try to improve the points you may have missed out on, whether they're in your GPA or your MCAT. If your GPA was borderline, it can be improved on by taking an extra semester of undergrad and retaking courses that were less than satisfactory, especially if they were science courses. This is a particularly sound strategy if your school allows replacement marks on their transcript. Some schools post only the highest grade attained for a course, while others post both or an average -- it bears looking into before you re-enroll. The second problem for potential medical school attendees is their MCAT score. If it's too low--and doubly so if your GPA is also low--then you need to retake it. Don't just walk in expecting different results, though. Invest in an MCAT prep program from Princeton Review or the like. Also make sure you get enough sleep and a good breakfast before you retake it--every little variable matters.
Another option is to enroll in another postgraduate degree in a similar field, like biology or chemistry. If you give a strong performance, you can transfer into a medical program. Alternatively, you can just finish a postgraduate degree and apply for medical school then--a master's or doctor of philosophy will make you a considerably stronger contender than those who just have bachelor's degrees. An MBA or a Ph.D in art history are, obviously, not quite as viable options.
The last option is to attend medical school overseas. There are a number of cheap schools in the Caribbean that take American students for less money and often without MCATs. This is a big decision that is not to be taken lightly. For one, even though it's cheaper, the price of going back and forth on holidays plus amenities like travel insurance will add up. What's more, if you want to practice in the United States, the pool of medical schools is considerably smaller. Even graduating from a recognized one will make finding a residency difficult.
If you attend a foreign school, you have two options. One is to graduate from it and take your chances on a U.S, residency. The other option is to attend for a couple years, show you are able to handle it, and then transfer to a U.S. school.