The second hand spring rates wont be right, and the front will probably sit higher than it does already because these springs are menat to support the extra weight of the 5 cylinder diesel.
If you are looking to lower the car, progressive springs are really what to go for. They will maintain the best ride and help prevent the suspension bottoming out.
I think some 147 sports springs are expensive because they come with modified wiring ect to keep the indicators at above the legal minimum ride height. That said, I don't know if anyone really bothers.
Go with a 30mm drop spring such as Eibach. They will maintain best ride quality, improve handling and looks. If you are not too demending a driver, or too critical about ride quality, then I suppose you could get away without dampers. I always recommend dampers, but I think all, or certainly most except the very first 147s came with the Comfort Pack suspension which rode and handled better due to softer springs and stiffer dampers. Because of this, you could possibly simply get away with the springs if you don't go too low or too hard. Be aware though that any lowering spring will make the suspension fell a bit more bouncy depending on springs. Alternatively, would could fit the Eibach Pro springs and dampers. As it is similar to the 156,this link may help
. Also, this link has links for cheap stuff too.
Going for a minimal drop means tyre wear shouldn't suffer. Some of the guys with approximately 60mm drop coilovers complain of inner shoulder wear due to increased suspension negative camber. Tramlining and instability are also increased.