Hi, Babyburr.
Is there anything wrong with your air suspension right now? If not, I'd suggest not changing it out right away.
IIRC, you tend to have most of your maintenance and repair done at a shop instead of doing it yourself. This means that you will pay more, since most shops sell their parts at "suggested retail" (and keep the difference) as well as charging you for installation. This is actually more than fair enough as far as it goes.
The "retail" price your shop would charge for the Arnott kit, as far as I can tell doing a quick internet search, is around $300 or so. The shop themselves would give you the "actual" number since it's their business. Figure two shop hours or so, and you're looking at $500-$600 for the job. Since the kit includes new fresh shock absorbers, there will be some time charged for replacing them, too.
Your shop might also have a "favorite" brand that they prefer over Arnott, and price it lower accordingly. I have no
personal experience on how good or bad the other brands are. Your shop will probably do a better job with a parts line they routinely install instead of a brand they buy one time for one customer, and that's if they're "able" to get the Arnotts at all.
"Most" (but not all) people who go for the coil spring conversion do so because it's noticably less expensive than replacing the defective parts on their air suspension with new air suspension parts. You can typically buy the Arnott coil spring kit for about the same price as
one Motorcraft air spring.
Others make the switch because the garage they took their car to are clueless on correctly fixing air suspension systems, and push the springs rather than learning the craft. If they charge you sixteen hours of shop labor, it's still a financial bloodbath even if they give you the parts for
free.
The rest, FWIW, convert to coils as part of major suspension modifications to make their Town Cars ride and drive like Crown Vic Police Cars or Mercury Marauders, and don't want to bother with finding air springs that would have the spring rates they want.
Back to most people buying the conversion kits, $600 is cheaper than $900 or more to replace both air springs, both solenoids, and both shocks with new ones. And if you're trying to make chicken salad on a chicken s??t budget, saving $300 or more to repair your car is something you can't easily ignore.
But the coil springs
don't ride as smoothly as the air suspension does when the air suspension is in good repair. They also don't level the car for both heavy loads and light ones. This won't matter so much if the system is completely shot.
But if it's working okay, or only
starting to go, you don't need to be in any hurry replacing the air suspension. This will also give you more time to figure out and decide if the smoother ride is worth the extra $300 to fix the system, if the system actually needs fixing. If you can tell the ride difference between the air suspension and the coils, buy yourself some happiness later by spending the money now. If not, than save the $300 for something you
will get $300 worth of enjoyment out of.
I would suggest talking to the shop you go to for your repair needs and getting a quote from them for the conversion, as well as finding out what brand(s) they recommend. Just for comparison, if your air suspension
is starting to go bad, I would also try to get a similar estimate to return the air suspension to a good state of repair. This will tell you what you'll
actually pay instead of getting a guess from "some guy on the Internet." Unless your air suspension is failing
badly or if you plan on driving on a long-distance trip any time soon, there's no hurry either way.
As for "turning off" the air suspension warning on your dash after the conversion,
@dave42's post has most of the ideas. You will likely
not be able to turn off the light in the PCM, and if you can you'll
probably need Forscan instead of the Snap-On computer most independent shops tend to use. In 2005, air suspension was standard equipment with no other options. Turning the light off in the PCM from what I've seen only works for the '10s and '11s where the air suspension was an option and the coil springs were standard. You
might have better results. "Fooling" the system as dave42 described will likely be much easier, so long as the solenoids, ride height sensor, etc are still in good repair.
Good luck with whatever you decide to do. Please let us know what you decide on, and how well it turns out.
Thanks.