You can race an SV for a season on two sets of tires. You can use pump gas. Racing doesn't get expensive until you start going fast. That will take about 3 seasons and probably more. Buy a well equipped SV race bike of the round tube vintage, and you'll be good for a long time.
Forget the big bikes. Even a slug expert goes through 2 sets of tires in a weekend. That's almost $900 in tires alone if you race Dunlop Euro spec.
Per Weekend Estimate
Figure 8 rounds with 4 races each - $260 in entry fees
Gas - 10 gallons + $50
Consumables over a season - $125/weekend
2 sets of tires over 8 rounds - $75/weekend
Lodging - $85
Water - $10
Junk food - $20
Beer - $12
Annual motor rebuild $2000/8 race weekends = $250/weekend
$887 per race weekend for an SV in your amateur seasons. Not bad. But once you get fast your tire bill changes everything because the cost per weekend goes parabolic.
Straight ahead and faster -Bo Weaver 1970
"There I was..." -Griffin Niner Three Hotel
"One day closer to a parade..." Jonny Gomes, spring training 2013