For £300 that's a bargain!
Important tips from someone who started DB about a year ago (though I currently gig so you can make a lot of progress in a year!):
Get it set up. This is vital, if it's hard to play you'll hate it and it won't sound to good. If it's already set up, great!
Get some good strings. I'd recommend d'addarios if you're on a budget. Helicore orchestral if you plan to do ANY bowing, zyex for that old school sound.
Get a teacher. You'll learn quicker.
Don't buy hundreds of books! I asked for loads of books last Christmas, and I wish I hadn't! Focus on one book, learn it, then expand your knowledge with a different book. Then go back to the first book and learn some more! I'd recommend rufus reid's book, and/or maybe ray brown's. Rabbath and simandl should, IMO, be studied later when you have a serious grip of what the double bass is.
Good luck! I'm sure you'll love the world of DB, and if you're ever in the East Sussex area (England) look me up. I'm friends with a few pro bassists and they love meeting new bassists!
Joe