Anything new around the $280 is going to be entry level and possibly not be very robust for outdoor mileage.
2nd hand, you will likely get something serviceable that will
a) allow you to see if you 'get the bug'
b) hopefully not need much money spent on it
c) will also hold its value, if you decide to give up or upgrade within a year or so
Ultimately you will be getting a road bike that's fine for fitness and will likely last for years with a bit of care and maintenance, but will be a fair bit off a performance bike.