I've been through a bunch of bikes over the years including both mountain bikes and road bikes and in my opinion if you are after a run around bike your best bet is to get something like an entry level mountain bike from one of the big manufacturers like Giant.
Throw a set of 1.5" slicks on it and you'll have a reliable bike for day to day.
If you think that you'll end up doing a more riding it's worth upgrading a couple of models up the range to get better components but otherwise just spend as much money as you can afford on getting a good set of lights and a good helmet. I've had my life saved by a helmet on two occasions and again i'd go with something from a big manufacturer like MET or Giro (the most important factor being a snug fit)
As far as getting a bargain I've bought $3500 bikes for $1500 on ebay and had to sell a $3000 mountain bike for $975. In both cases the bikes had seen little use and the bike i bought for $1500 went on to do several years of weekly rides without problems.