Could Someone Please Help Me Negotiate With My Parents?

So...here's what happened. Back in March of 2009 my boyfriend left to take a job teaching English in South Korea. Being as he's been the only boyfriend I've ever had and also being as I had money that I had been saving to go on a trip that got canceled I was able to go and visit him last summer. As happy as I was to be with him I was sad again when I arrived back in America...I also had my first semester of college this year and it was "interesting" to say the least. My first roommate tried to get me kicked out of college on false accusations of vandalism (I was at a club meeting when she said that I poured cough syrup all over her belongings and that the syrup belonged to me which it didn't...I don't take drugs) and also send strange men into the room when I was by myself at night. Luckily I got switched out and while my next roommate and I got along without issues she was using/selling drugs and was cutting herself and leaving the towels she used to clean up after wards all over the room. To top it all off I was taking sopre level cles right off the bat...what kept me going throughout all of this was that I thought I was going to get to see my boyfriend during Christmas break. I soon found out that when my parents told me to "just wait" when I asked them back in late August/early September they never planned on helping me go back. I felt like they had lied to me when they had told me that we'd talk about it later instead of telling me that they weren't going to let me go back in the winter. When I came home on Christmas break I tried to talk to them again and they forced me to agree that I wouldn't be allowed to go in the summer unless I had a job lined up...I tried to explain to them that it's January and no place is looking for summer employees right now, the 2 places that actually gave me a date when I could check back for summer jobs was around Mother's Day...that's 4 months away and during that time my finals are occurring so I can't really look that week. After much negotiation I got my parents to agree to let me purchase a ticket even if I didn't have a job lined up after winter break. I then found an affordable ticket ($1000) to Korea and I have the money to pay for it and my spring semester fees but now they've gone back on their promise to let me go...they say that if I go at that time I won't have a job for the summer even though I have a source of income (a dogwalking business). I feel upset that they've lied to me twice and that they've told me that "it's your money" and "we won't stop you" but still refuse to let me go. What should I do...talking to them and explaining why I feel the way I do doesn't work and they say I have to have a job before I buy the tickets...if I wait to buy the tickets until 2 weeks before I go they're going to be about $3000 and I know I can't afford that. Please help me!