What kind of overflow do you have and whats your head height. Use those to items to calculate the maximum flow rate comming out of your pump that you can have with out overpowering your overflow. Then pick the pump that is the 'best fit'.
For example if you have a standard U tube overflow with a single U tube then your max flow rate is close to 700GPH and a mag 9.5 would be just the right fit for you if you had the normal 4' head height. If your 90 has internal overflows then you can process more water per hour than a standard hangone so a mag12 would be a good fit or even dual 9.5's. But then you run into your $100 budget limit.
Mag pumps are great pumps not only for the money but they are acutally relyable.