I'll give you the low-down. The fatman kit does cost a bit of money, however, if you add up parts from all the other alternatives, they all cost a lot of money. Examples, Global west kit costs ~$1000 just for the upper and
lower control arms, no disc brakes, rack and pinion, and without the strut rods. TCP coilovers cost $2000+ and don't include steering or brakes and you can't do anything to the shock towers if you so choose. RRS also has a strut style
suspension like the Fatman, but it doesn't include rack and pinion or a tilt column. Also, with RRS, you need to use their stuff, ie. rotors and calipers and struts, and they don't make it obvious as to whether or not you can buy replacement parts at the store on the corner. Mustang II from Heidts is well known. Their kit costs over 2000 and gives you rack and pinion and disc brakes, it even lets you completely get rid of the shock towers. However, a lot of fab and welding is required to install this system and it moves the engine up and forward causing hood and radiator clearance issues, not to mention an undesireable shift in engine mass forward. It's not easy if you choose to return your stang to stock after this is installed. There are more out there that also cost the same or more for less features.
Second point, not all is good with the fatman kit. The steering kit that is included in the setup is to fit a tempo escort rack. The input to the rack is very close to the middle, so the steering column shaft practically runs through the engine, forget about anything other than stock cast iron manifolds.
Third, if you're shaped anything like me (6'1") not having a tilt wheel sucks, which the fatman kit also provides you with. Not to mention you can buy spare parts at Ford, Checkers, or even the salvage yard if you want to save money.
I have seen The Mustang Shop install this kit on several different year Mustangs. It is a very good shop and I know of 4 of their mustangs that have been featured in mags like Mustang and Fords and Mustangs Monthly. The biggest and only criticism from them is that of the use of a tempo rack. They have actually improved upon the design and have made a rack that utilizes a Taurus rack and pinion. This setup even cleared the 03 Cobra motor and provided excellent handling, and braking.
I hope this helps and I have done extensive research so if there are more questions I can try to help.