Olnick is correct - get rid of the air suspension (far too cost prohibitive to try to repair/replace) and put in standard struts & springs. Easily done with parts sourced from a junkyard or in the marketplace here on the USMB.
I had to do this with my 1990 LS wagon - the rear air struts were completely shot when I got the car. (your picture looks exactly like my car - right down to the color! only yours is in much better condition LOL)
Parts list consists of: Struts, coil springs, & top hats (upper strut mounts) to fit your car. You should be able to source the complete assemblies (all the mentioned parts together) fairly easily. Please note that each is specific to a location - LF, RF, LR, RR
Once you have all 4 assemblies - simply remove the air struts (a pair of side cutters make short work of the air lines), and replace with the standard coilover struts.
You will need to remove the upper cover inside the car, over the rear wheel well. On mine it was a speaker grill & speaker that had to come out to access the strut mounting area - not sure if yours still has the rear speaker in that location - but if it does, just pop the upper cover off (the grill portion should be a seperate piece) then unscrew the speaker, disconnect the wires and set the speaker aside...there are 3 studs/nuts that hold the upper mount in place & 2 bolts that hold the lower end.
On the front lowers - mark the position of the upper bolt - it is a cammed bolt that adjusts camber - by marking its position, you can get it put back in pretty much the exact position it was in avoiding the need (and cost) to have an alignment done.
to prevent the compressor from kicking in - there should be a small control box under the drivers seat that controls the air system - simply unplug it (there may also be an associated fuse in the fuse panel - it has been about 6 years since I did mine, so I dont remember everything). compressor is hidden behind the left front fender - if you feel ambitious, you could remove the fender and take it out - I just left mine in place - it isnt hurting anything by being there. The button on the dash is still in place as well, it just doesnt do anything anymore.
by making the switch to standard coilover struts, it also gives you the option of adding a little extra height by using Forester struts/springs - but you would still need to have the correct top hats for your car.