A couple of suggestions to the OP-

1. Look for any local bike shops (LBS) that carries used bikes, or has rental bikes. You might be able to find something in your budget.
2. Find out if you have any co-op's in your area. Again, great resource for finding decent rides at a decent price.
3. If you liked your dad's Giant (which model?) so much, and IF it fits, maybe work out some sort of lend/lease deal. Could be the old man has been looking for a good excuse to buy himself a new bike (w/o the wife giving him the 'look').