Inexperienced needs some major help on writing tiered structure formula!

Hey all. I need some major help. Ill try to explain this the best I can and attach the best example I can.
Basically what I am wanting to do, is be able to put in last years sales under the LY column (example attached) and have the incentive structure auto calculate what the potential bonus would be if a 5% increase is met, 10%, 15%, 20%, 25%, and 30%. The way this works is noted above PLUS 1/4% of total sales. (.25% of total sales, not 25%).
So between 25k and 50k with a 10% increase would result in .25% of total sales plus $150.
Anybody who could get me on my way, it would be greatly appreciated!
I usually love doing this stuff but for some reason, I'm having major difficulties.
Thanks so much in advance!