Youre not going to be happy with a $100 metal detector. Well, not once you learn your way around the market.
In the lower price range, I'd recommend something in the Garrett Ace family, probably no lower than an Ace250. I'll let others that know these machines better than I comment on which Ace would be best for you.
I tend to separate detectors into 3 price ranges: entry, middle, and top. Garrett Ace series for the first, the Garrett AT Pro in the middle, and Minelabs for the top are my goto recommendations.
Also, remember that the advertised price that you see isn't the real selling price. Dealers have some wiggle room. Also beware of junk that dealers like to throw in to make a package appear more valuable. imo, you need:
1) a detector. duh.
2) a Garrett pinpointer (~$120)- don't cheap out on this, its very important.
3) a digging tool. garden trowels aren't strong enough. most folks get a Lesche or Gator.
if you beach hunt, a good scoop; but we'll cross that bridge when we get to it, eh?
Everything else is 'nice to have' and can be added as you see fit, but I wouldn't start with less than those 3 things.
Dealers. I think youre gonna be pleasantly surprised on how nice metal detector dealers are. I haven't met or dealt with one yet that I didn't have a good experience with. I think this hobby attracts good people. Start with one that sponsors the forums. And if theres one near you, Go See Him/Her!!! Swinging a machine in a store can tell you a lot. Also look for a local detecting club and go to a meeting. Folks will gladly let you swing their machines to see how they feel (and they will brag on them. a Lot). Usually a club will have a dealer or 2 as well (double good). And lastly, I will tell you the dealers whom I have had good experiences with via PM if you want.