I have a 40 year old 10 speed road bike. It still works but is heavy and the gear ratios I feel are not the best. I would like to get into something more updated. I live in Florida and can ride year round. Not many mountains here. I ride 30 to 50 miles a week for exercise. All of it on the road. It would be nice to have something lighter, easier changing gears, and with better brakes. What I don't have is $600 to $1200 to spend on something new. Are there any good used bikes in say a $300 range that would be worth having? Or what would be top priority as I look for a used bike? What brand of gears, brakes, etc. I am 6 feet tall, weigh 235. Have already lost 35 pounds and looking to get to 220 where I will be very lean. Any advice would be greatly appreciated.