Need a bit more information - other than the drop, anything else that you need to have with the coilovers?
- ability to adjust the ride height quickly, remotely - or do you plan on sliding under the car to adjust the ride height
- remote control (manual or electric) of damping characteristics
- thoughts on what spring rate you want to run (ie, just daily, or possible track use down the road)
- what size tires/wheels are you planning to run, offset, plans for extreme camber
Budget is relative. For some - $600 to $800 is considered high, others can go into the thousands. Unfortunately, quality manufacturers (Cusco, Whiteline, TRD, etc.) of coilovers for the 6th gen Corolla are extremely pricey - if you can get your hands on them at all. So not just a matter of cost, but also availability.
That said - there are a number of possibly options. The E90 chassis will take coil-overs from the later generations. If I remember correctly, E90, E100, E110, AE92, AE110 are interchangeable. Granted not 100% direct swappable - might have to mess around with brake lines, etc. But the main bolt patterns should be a direct fit. You can ask the vendor for cross-compatibly to verify.
Options:
- Megan Racing and KSports are considered decent coil-overs (best bang for the buck) sort of thing. Pricing is on the order of $600-$1200 - depending on spring rates, adjustability, etc. This would be the simplest option - basically drop in, adjust height and go. If you can change struts and springs on the car - coil-overs would seem way easier to install. Some have the option of EDC - or electronic damping control - so you can control the characteristics of the strut (rebound/compression).
- Ground Control or Cusco sleeves are another option. You'll have to do some modifying / some fabrication work - but costs can be quite low - looking in the $200-$400 range. Matching the spring rate to the strut is the key here - if there is a mis-match - ride will be terrible, handling will be poor. Sounds like a hack compared to legit coil-over setup, but matched correctly, these can give you more flexibility than a traditional coil-over setup.
- Another possibility - airbags. Owners that want the most drop, but still retain the ability to return the car to stock height or even higher - can't beat the flexibility of airbags. Here, installation is the key - if installed correctly, will last as long or longer than a conventional coil-over setup. You also gain the ability to control ride height remotely - just by controlling the valves and air compressor. Costs will be similar to a higher end coil-over setup - depending on the condition of the car (ie, rotted unit-body or weak attachement points, they have to add plates to beef up the bottom). You won't be taking this sort of setup on the track - but for a daily driver that wants to go really low - airbags are the only way to go.
