In my opinion a "cheap" handgun is a no win situation. Get a nice used 12 ga. shotgun, stoke it with 00 and your good to go.
Eli

Used Glocks can be had for around $350-400.
Accessories are far more available, to include magazines, holsters and such.
I'll try not to bash Hi-Points, even though I've seen why they deserve it first hand (yes first hand accounts) but please, your money would be better spent on a used Glock.

The Sigma's run into a similar problem as they really aren't a "popular" gun, so finding magazines and holsters is more difficult than for a pistol that's used all over the place.

You'll end up spending a crap load of time, effort and money on accessories for pistols that are less "popular", which means you'll have even less money for ammo to practice with and practice is far more important than any of the above.

I, too, suggest you buy a used gun. You'll get more bang for your buck.
If at all possible, get a return guarantee. Then take it to an independent gunsmith for a look-over. Fire a magazine-full out of it. If it works well and it feels good in your hand, keep it.
If it doesn't work well or doesn't feel good, return it for a refund against the next used pistol you're going to try. (That way, the store has a reason to try to please you: They get to keep your money.)

Whatever you end up with, get at least two extra magazines for it. Three is better.

Then, go out and practice with it. And take a self-defense course, if you can.

Might want to look at a Ruger P95-full size 9mm. My brother picked up one for $299 and it's a nice accurate shooting pistol.