Well pricing varies from city to city , state to state, so I can not tell you if that is fair for your area. It would be fair priced if you where in my area. The plumber can get a idea what type of pump you have in the basin by looking at the cords. In most cases its a faulty switch on the pump but replacing the switch can be costly and would be cheaper and better insurance to replace the pump.
Now about builder pumps being not so good, that all depends on the builder and what they specified from the contractor. Most cases around here they use Zoeller pumps which is a very good pump. One thing I have noticed if all they did was rough in for a bathroom and no fixtures where installed, the contractor will save himself a buck and install a sump pump in the ejector basin. Then when people finish the bathroom off, the do not know about the sump pump in the ejector basin and it works fine fir a while till the pump gets clogged with waste. The pump that should be in the pit with a bathroom dumping into it should be a 2" discharge ejector pump.