OP, don't forget that there is also a labor cost for installation, so do it right the first time and save yourself costs down the road.
You can't just add springs. They lower the car, so your oem shocks are not designed to handle the new ride height. Means you are looking at new shocks within 6-12 months, the ones that match the springs! That's why a set of $1,000-1,200 coilovers are worth doing. That price range is competitive with a new set of sport springs and shocks. Install is same either way.
Audio: Jehnert Flatline speakers, Mobridge M1000 DA2 prepro, Helix P-DSP, Zapco Z-150.6 amp, CIC iDrive upgrade
Performance: MHD Pro Tune, AR Downpipes, ER FMIC/CP, DCI, RB turbos and inlets, KW V2 coilovers, Fuel-It Stage 2 pump w Ported fuel rail, Mfactory LSD