wait until jan, you will find some at ebay.co.uk or amazon.co.uk, I bought my 550d from amazon, they have great service and good prices
With a DSLR you will have a great tool to learn all you need to know about exposure, composition etc. I'd wait until you've mastered the technical stuff before buying any toy cameras. (Lomography, Diana, etc.)
You will then have the knowledge to be able to work with the quirks and limitations those film cameras have. You might otherwise find yourself frustrated with your results and the waste of film and money.
There are two pips in a beaut,
four beauts in a lulu,
eight lulus in doozy,
and sixteen doozies in a humdinger.
Nobody knows how many humdingers are in a lollapalooza.
I found a Nikon D-3000 refurbushed for $3.00.00 at CAMETA CAMERA.COM
Based on what you say you are currently taking photos of and what you are trying to get into, I would suggest a mirrorless slr. My personal choice is the Olympus brand. The Pen series gives you all the control you could want with Manual, Aperture Priority, Shutter Speed Priority and Program mode. It also gives you numerous automatic settings and "art filters". So, instead of buying a Diana F+, you can use just one camera and use the art filters instead of film.
Also, the Pen series has numerous lens adapters available for it as well. I own the E-PL1 and bought the Canon FD lens adapter for it. I picked up a 200 f/3.5 for $40 and it works like a champ.
Another thing to consider when buying a camera. Are you going to want to lug the D3000 and the associated equipment to gatherings and other functions to take your photos? Not only are they big and heavy, but they are rather intimidating to the folks you are taking photos of. The mirrorless cameras are smaller and easier to carry around, and when using them, folks don't think "here's old so and so pointing his camera at me....AGAIN".
Just some food for thought. Good luck, regardless of your choice.