Can you get something on the cycle to work scheme?
http://www.cyclescheme.co.uk/
Means the cost thing is a bit more manageable. Or what others have suggested, another set of wheels (or even just tyres) for the current bike while you get used to the ride and distance.
Rucksack, good lights (multiple cheap(er) lights are better than one super expensive set), always carry a waterproof and a basic toolkit (mine live in my rucksack permanently so I never use them on another bike and forget to put them back after a weekend!).
Leave as much stuff at work as possible, take in underwear and a clean shirt each day. Wet wipes, towel, deodorant and you can have a decent wash in any bathroom.
This is worth a look for advice, tips etc on commuting:
http://www.britishcycling.org.uk/commuting
The related side of that is…buy a membership of British Cycling, the legal side of it comes in handy if you get knocked off!