am i entitled to full compensation?

What is the name of your state (only U.S. law)? Ohio

In January of this year, I booked a return trip ticket from Pittsburgh to Barbados (via Charlotte) for June 28th to July 12th for a family reunion, with Expedia.com. The carrier was USAirways and the ticket cost $730.
On my way to the airport on June 28th, I received a telephone call telling me my flight from Pittsburgh to Charlotte was delayed due to technical difficulties and that I would now miss my connecting flight to Barbados. Obviously distressed, I called Expedia (as this was the only contact number I had on me). They got on the phone with USAirways and their representative told me the only options I had (as there were no more flights from Pittsburgh to Charlotte) was to either fly the following week or to take a full refund.
I took the full refund because I was desperate to start trying to find a new flight with another carrier.
I phoned American Airlines immediately and explained the situation. They informed me that USAirways should have offered to find an alternative route, even if it was with another carrier. I phoned USAirways back and they basically told me they didn't want to know as half an hour earlier I had taken the refund, which was my only option as far as I knew at the time.
I finally, after an hour on the phone to AA, I managed to get a flight that would get me in on the following evening (29th). The cost of this ticket was $1230.
I have ended up $500 out of pocket and missed 36 hours of precious time with my family. Not to mention the emotional distress, as there were more problems with the flights on American Airlines, who cancelled one of the flights, booked me on an illegal connection and I almost missed my final flight to Barbados.
I wrote to USAirways and they have sent me a $125 voucher as a "gesture of goodwill".
However, I am still $375 out of pocket.
I do not think this is fair, and am continuing to write them letters to try and get the full difference in price of the tickets.
I would like to know if I have any legal standing here. Any help is much appreciated.

Thanks

what is an illegal connection?

an illegal connection is when they do not have a sufficient amount of time between flights with the same airline. Domestic times are 35 minutes and International is 45 minutes. In this case, I had 35 minutes between my flight from Pittsburgh to Miami and Miami to Barbados. Therefore it was an illegal connection. Luckily for me, both flights were delayed by an hour and I arrived next to the gate I needed to be at, so I made it... just.