Very broadly speaking a pump is gonna be more reliable, they have fewer moving parts and don't rely on the ammo to cycle the action. If you want to spend the least amount of money, a pump action from a reputable name is hard to beat - I'm a Mossberg fan personally, but there are other good brands too.
That said, my $300 Turkish semi auto (asena zr7) has been very reliable for me. Would it stand up to a 10k round torture test? Probably not, but it cycles target loads and steel loads, and has killed a bunch of grouse and ducks, which is all I could really want from it.
I'm also not suggesting every $300 Turkish semi is this reliable. Maybe I just got lucky, maybe this particular model is a good one, I'm not sure, my point is you don't HAVE to buy a Benelli or Beretta to get a decently reliable semi. If you've got the budget then you're going to have far less chances of trouble with brand name vs cheap Turkish though.