You can go to Home Depot and get a trash pump that will work fine for... a year? But, for 40% more you can get a Yamaha self priming pump that won't let you down for 10 years or more. You can even abandon it for months and months and it'll start right up on the first or second pull. Let's face it, when you need a trash pump, it better work!
There's really two things that make a trash pump reliable: its carburator and the pump housing.
-The carb is where the manufacturer can save a lot of money because even horrible carburators will run fine when they're new. But, try starting it a year later and you're wondering... What the H$%%! Yamaha's engine design has a reputation for reliability, even under the harshest conditions.
-Composite pump housings are great cause they're so cheap to cast. But one short mistake and they warp. Yamaha's trash pumps use alloy housings that'll withstand reality. It's that simple.
So, there are cheaper trash pumps around, but the one that'll save you the cost of two or three replacements over the next 10 years is the Yamaha. We could sell the cheapies, but the Yamaha doesn't let anyone down.