There are always amazing deals in the Amps for sale section on this website, my Hartke stack sold for £300 and that was a 4x10 paired with a 2x10 with tweeter! amazing tone very sorry to see it go. It was also my first "stack".
Soundwise you could probably try a larger 15" or 18" speaker cab with a 2x10 on top i was amazed at how much punch and mid/top end i got from a 2x10 great for projecting your notes clearly and precisely you can easilly pick both up at about £100 each or less, leaving you £200 for a head which is more than enough for a 200 - 300 watt head second hand!