All the payments and insurance and extras for the entire year, or just the summer? The payments and insurance continues 12 months a year, but the gas savings can only be counted on for the riding months. Of course, the number of riding months varies by location.
I'll say it again ... if you want the bike and can afford it, then get the bike. But you are almost certainly not going to save enough money to actually come out ahead. It might come close or even pull a little ahead, but it's not going to be enough make a dent in your finances.
I averaged cost out for year ‘round, but calculated my savings based on actual riding time. over the course of the year (only counting normal commute miles) i came out ahead by enough to make 2 extra payments.
if i counted in my vacations where i took my bike instead of my truck that would add another $4-500 in gas money saved.