Thoughts:
I agree your estimate for safety equipment is low. Pretty much double any estimate you come up with. Such is the life of a speed freak.
For me, helmet, firesuit, gloves, shoes, were about $2000 alone, but I'm legal for any speed, and fire safety is very important for me. Chute, 2 fire systems, window clips, roof rails, window film were about another $2000. Seat, padding, harness were $500. Cage? Not sure how much. It was over $3000, but I used chrome moly, and twice as many bars as the minimum requirement, and I had someone who is very good with TIG and cages do it (Mitch, the same guy who did the Hot Rod Magazine Special). Keep in mind the SCTA cage rules are NOT the same as NHRA, so if you are going back to the dragstrip ever again, read both rulebooks before starting.
And tires are problematic if the existing record in your class is over 200. There are very few "cheap" LSR tires. If you can find a class you can run that is under 200, you can run cheap speed rated tires. Or run time-only up to 199.999.
Sea level HP is not the same up in Bonneville. It's about 6000-7000' DA in August. I don't have concrete #'s, but often N/A car will add .7 to 1.0 second drag racing at Bandimere (6500'?). You can run higher than normal compression in thin air, and you'll have to jet down, and advance the timing. If you can spend a day in SLC at a dyno shop for tuning, it might save you some time.
Might sound like a hassle, but it is worth it. To race along side some of today's premier hotrodders on the legendary Bonneville salt cannot be described by words or pictures. If you are gearhead, you will be in heaven.