Local self-serve wreckers are your best/cheapest bet if you just want a scissor jack. I stuck with a scissor jack for a long time and only a few months ago did I start using a proper hydraulic jack. Got a 2-tonne won which is overkill for the Micra but isn't when working on mate's cars and it's good to have the security of it being a strong, well made jack...
THAT SAID, I've bought a second-hand jack from the wreckers and after starting to jack up a mates car, the damn thing bent at the base when it was halfway up. No damage, but the lesson was clear - if you're going to be using a jack more often than just when switching tires, a decent hydraulic jack is a worthwhile investment.
Food for thought..
---dens