Springs and old dampers don't work. I've done it . Had a set of p1 springs plonked on the old dampers . It was like sitting on a washing machine at full spin . I'm afraid you won't get to keep the nice ride and go cheap on a set of £50 springs. Anyone says otherwise is talking out their backside .
Plus bare in mind the sumps on these cars are fairly low already . Mines sitting at about a 50mm drop . I stay well away from speed bumps .
Take in what Damian has said . If it's a cheap
lower job - hard ride and soon new dampers .
Coilovers - yes aprox £100 more in cost , but 1- lowered , 2- better ride 3- saves money in the long run .
If you can't afford it yet then just wait a little longer mate .