@RadioLu You'll have to go for a houseshare or flatshare as a student, the more central you go, the more expensive it's gonna get. And regarding the oyster card, you do pay smaller fees if you are a student in London so you should probably have a look at that, because trying to avoid the Tube is impossible; it's convenient and fast (but expensive I know). I'm in Canary Wharf so it's an easy commute (though I wouldn't do it by bike) but from farther away, it can be quite a pain.
But student halls are an absolute rip off, just don't go there it's crazy expensive.
Regarding small hacks, I always do my food shopping online and get my groceries delivered; it's easier to manage my budget, and I can shop the offers real easy. Also as a student, create a Unidays/Student Beans account and perhaps try and buy a NUS card, it'll get you many discounts that can be helpful.