Mine cost me about $2500, but that's because I was an idiot and didn't put enough fluid in it. Fried my clutches, but not because of the J-mod itself. I'd already done it once before with my Mustang, but I got a bad case of stupid the second time around. Fortunately, my T-bird is a hobby car, not my daily driver that I depend on for everything.
Read the articles completely, get the right parts, don't overdo the HP levels, and take your time. It's easy, but if you've never even dropped a transmission pan, then now probably isn't the time to start unless you have some experienced assistance. Especially if this is your only car. I'd be leary of a shop doing it, unless you are 100% sure you can trust it. Good luck finding one that will, unless you live where there are a lot of Ford tuner shops.
97 LX, 4.6, Dynomax catback, Mustang MAF/intake tube and Aviator throttle body, Xcalibrator2 by Lonnie at BOC, 180 t-stat, Super Coupe wheels with 235/60/16's, Kenny Brown strut tower brace, Tokico Blues, Eibach Pro-kit, some strategically placed MN12 Performance polyurethane pieces, '02 Grand Marquis transmission
Submariners do it deeper...