I love my zebra nerite! He is an awesome algae eater! I paid $3 for mine.
As for the trumpet snails...do you have sand? If not, there's really no need for them. They breed like it's going out of style, as well. I am STILL picking them out of my 55gal and I removed the play sand from that tank a couple of months ago and rinsed the whole tank REALLY well. Start out with "a few" and you'll end up with MILLIONS in a couple of months. Trust me. Been there, done that.