You will not need many tools to start with and can get more later so don't put too much aside for that. I started with one morse taper sleeve and one end mill. Even a drill chuck can come later. Sure it is nice to have an ER or Clarckson chuck, a rotary table, a dividing head, a boring and facing head etc. but stinting on the main machine would be an error.
Bear in mind that delivery can be extra and can be a problem with second hand machines. However one trader does keep advertiseing pallet delivery for £65 so cheap deals are possible.
It is worth thinking about the move from front to shed in detail. You might want to invest in 2 scaffold planks (to saw in half or get 4) if the path is not flat paving and some scaffold tubes to also saw to length or perhaps some wheels. A normal pallet needs modification and strengthening to run over rollers but you can take bits off most machines to make it lighter. I once got a quarter ton+ machine down to 350lb to move it via the living room.