While the website you linked is my favorite OEM parts site and usually has the best prices around, I would not use them for this... Your estimate is actually way off. There are
two retainers for each flare for a total of 8 to do all 4 flares. You also need the 24 M5x.080 nuts with washers to secure them with and the 4 screws to secure the flares where they wrap under the body. Altogether, you're looking at more like $200+. Here's the part numbers for your '99 if you're interested:
55155674AB x1 (Front Right Rear)
55155675AB x1 (Front Left Rear)
55155676AE x1 (Front Right Front)
55155677AE x1 (Front Left Front)
55155678AC x1 (Rear Right Front)
55155679AC x1 (Rear Left Front)
55155680AC x1 (Rear Right Rear)
55155681AC x1 (Rear Left Rear)
J4200408 x24 (Nut w/ Washer)
6035322 x2 (Screws Front)
0153185 x2 (Screws Rear)
If you don't want to hit the junkyard, I'd post up a wanted ad here on

. Lots of guys take off their flareGreat! s (and retainers) so they can trim their fenders. I'm sure they'd rather sell them to you than toss them in the trash. The studs are known to break off pretty easily but if you find some that are not located in a rust prone area, you just might get lucky and find a complete set. Good luck!