You can make your own nasal rinse with 1/2 tsp salt in a cup of water. I found a recipe that called for adding 1/2 tsp baby shampoo which helps break down the coating on bacteria. I've used the recipes and found them effective with and without the shampoo, for myself.
Even the "Netti Pot" (I use a small ordinary teapot) doesn't get up into all the sinuses. I can't get anything to go all the way up to my frontal sinuses. I think they are blocked from having my nose broken and septum displaced.
You can re-use a spray bottle, but you should thoroughly disinfect it! Straight bleach works fine, but rinse well. Even the Netti Pot needs to be disinfected every time you use it, or you'll just reinfect yourself. Don't save any solution in a container that has gone into your nose.