What you actually want is 3+2 which Like Christian points out is way different to true 5 axis machining.

But anything done with 3+2 setup can be done with just 3 axis and fixtures/vises. 3+2 is just easier.

Forget those Ebay offerings for anything but learning because they just are not strong enough for cutting anything harder than frozen Mars Bar's.
The Linear components match the electronics on quality or lack of.! Structeral Design is very poor which would result in more chatter more than naked Ozzy in Artic snow storm.!!

In all honesty you'll need minimum of £3K to even build any half decent machine with 3+2 capabilty's able to cut steel's. You'll need at least double this to buy any pre built machine worth having, if you can even find one.!!