I wouldn't even consider carrying something less than 400 ft-lbs for self defense. I finally found a good 44 load which I clocked at 1,100 ft-lbs.
Now we're cooking with gas.
A Freedom Arms Model 83 revolver shooting the 240 grain hollowpoint .454 Casull puts out over 1,900 ftlbs of energy. Although I hear a new one costs about $2,000, but you might be able to get a bargain on a secondhand one. Of course, .454 Casull ammo costs up to $30 for a box of 20, so target practise would be expensive too. But it must be very satisfying watching a mugger or a burglar's face after you pull one on him!