I've had lots of b/w 2d sonar units, but never really liked them all that much so I just basically used them to tell me depth. A few year ago I bought a color DI unit 5" (Lowrance Elite 5DSI) and loved that unit. Broke a pin in the connection socket & had to replace it with something else (out of production at that time). Caught the Hook 7 on sale and been using it since. Still don't care much for 2d sonar, preferring Down Image .... but, I can combine the two with this unit, if I want.
Now the Hook2 series is out, but I'm not sure what the difference between the two generations is ... but the pricing is close to your limit.
If I didn't really know what unit I wanted, but knew my max budget .... I'd probably contact Brian@BBGmarine and talk to him. Seems everyone that has done business with him has been pleased with the price, speed of delivery, customer service, and his overall knowledge of the units.
Me, personally, I wouldn't go back to a 5" screen (or smaller), especially with a DI or SI capable unit ...