1. Know your seats.
I am cheap, but that doesn't mean that I buy the cheapest grandstand tickets out there. The cheap tickets are usually worth what you pay for them. On the other hand the most expensive seats are usually not worth half the price they go for. The most expensive seats in Montreal are on the main straight which gives you one of the worst views for a grandstand seat. I sit in grandstand 21 which is $100 cheaper and gives a view bettered only by grandstands 11 and 12 (I would think about moving but I watch with some good racing friends and we have front row seats locked up)
2. Don't buy things.
This sounds overly cheap but everything at the circuit is a rip off. Food is expensive as well as being bad. I prepare food in advance to bring along with me, but if you are staying in hotels I would recomend finding a supermarket to save yourelf $20 and a case of food poisoning every day. The same can be doubly said for beer and water. I always take 2 bottles of frozen water and half a dozen beers in with me. After that the beer gets too hot and you have to bite the bullet and buy budweiser in $6 plastic cups.
3. Support crappy teams
Anything with a Ferrari or McLaren logo on it is going to be overpriced. Why not be a Spyker, Super Aguri or HRT fan. The clothing is half the price and everyone will know that you are a real fan. I often buy clothes from the year before which they usually have in a cardboard box beside the main sales. It is also a good idea to check out merchandise online for last years clearance. I just bought 2 t-shirts from the Montreal 2010 grandprix for $10 each off the circuit Gilles Villeneuve which would have otherwise been $25.
Other than those three tips I am afraid I can't defend you wallet much more. Eventually you will find that going to motor races is pretty damn expensive. If they weren't so much fun I would stay away and hitch hike out to Formula 1600 race meetings.