Not seen the Bullistorm's for less than £45-50 recently
As Neal said, with that sort of budget, a used speedo is the way to go. The older Sphere LRP (or Nosram Equivalent) and Novak GTB's are still OK and sell for £30-40 usually.
As for a motor, if you can get one off someone you trust, I'd go for a higher spec used unit. If not, try squeeze the budget to £50ish for a new high end one. I have in the past bought new budget motors, and never been impressed with the length of time they lasted before needing replacing. I think the HPI ones are around £50 new or I have seen Team Wave ones (These are a Relabelled Version 2 Speed Passion unit AFAIK) for around £40 new.