NA power is expensive. Really expensive. You *can* do it, but you also need to realize that any turbo kit will be cheap in comparison to NA power. If your goal is to pull on stock mustangs w/o any forced induction, I would personally recommend:
1. Displacement. FUCK B16s!!! If you're gonna fight with a 302 or 351 stang NA, play by stang rules. THERE IS NO REPLACEMENT FOR DISPLACEMENT. GSR, LS/Vtec or CRVtec would all put you in a much better place.
2. Cams. FUCK JUNK2!!! I'd rather stick a Skunk2 cam up my ass unlubricated than in my car. Junk2 = the most hyped overpriced NA cam there is, IMHO. Toda B or C or RM/EF1 M22-M24e depending on your goals. And don't even get me started on Skunk2 valvetrain... A good friend of mine's click all used Sk2 valvetrain on their Euro ITR motors - 5/6 motors is now dead <1.5 years later from valvetrain failure. Plus the premature wear on retainers, plus, plus, plus... Valvetrain really is key because being able to rev a honda motor is also one of its real strengths.
3. Compression. NA power = high compression. There isn't another polite way to say it. You can run 12.5:1 piston compression on pump gas without headwork - I know because I tuned fucker's car. If you're limited to 91, you probably want to stay below 12. In any case, higher compression will help you make up the 5.0 - (2.0/1.8/1.6) difference in torque without having to spin the motor to 15,000rpm.
4. Airflow. Power comes from combustion. Combustion requires air. Put more air in, get more power out. Sound simple? ha! All big numbers NA cars have serious headwork done to them. The only exception I could see to this are the DC5R motors that flow 280CFM/port from the factory. The EF1/RM 200WHP B16 may have had an essentially stock bottom end, but it had *amazing* portwork. If you forget for a minute that airflow is what makes your power with a NA setup, you are a fool. The portwork will break the bank, but it is also where the real power is to be found, IMHO.
5. Pumping. The motor is essentially an air pump. If you do things to help it pump air more effectively, you're going to make more power. This would not be limited to: 2.5"/3" exhaust, ***SCAVENGING HEADER***, well designed plenu intake, ITBs
6. Tuning. You're going to spend days, if not weeks tuning a high power NA motor. If you switch to a ITB setup, double that. Serious portwork will help you make the serious power, but it also totally reshapes your VE curves, requiring you to completely retune the car even if you had kept the same cams. Change the cams AND do headwork while upping the compression and you might as well start over. Switch to ITBs and you'll probably be in the realm of a DFI7 or Motec, and even further lost. Point being: lots of time to get it right child.
So, does that expensive turbo kit sound any cheaper yet?