Lancaster and Goldsmiths are very different in terms of Fine Art, the main difference being that the former is much more structured (with briefs and such). If you're set on making a career as a fine artist, Goldsmiths would be a much better choice as the course is firmly directed with this in mind. There are also so many opportunities to exhibit and share your work in London, as well as gaining experience in galleries.
My only expirience of Lancaster is from the open day, but they really seemed focused on more realistic career paths and the academic side was quite dominant. But that doesn't mean you'll never succeed as an artist if you go there. I think the best thing to do is pick the course that you feel is the best fit for you.
Also, I've found living in London isn't as expensive as everyone thinks if you know where to go. But rents can be pretty ridiculous and I can see that international students could really struggle. If you do decide to move to London, maybe try to find a room in a house-share rather than halls. Sometimes you can find basic rooms for around £90 a week.
Good luck!