[PC] Steam - FIM Speedway Grand Prix 15 (rated 91% positive on Steam) - $3.93 AUD - GamersGate UK

While not the all time lowest price, this is pretty close to it and the best price currently available (Steam has it for $5.79 AUD at the moment).
For fans of Speedway racing this is definitely a must buy game. Apparently, the learning curve is quite steep so do not buy this if you expect an arcade racing games where you can win your first race within 5 minutes.

From the website:

Tremendous power and no brakes! Experience the thrill of speedway! FIM Speedway Grand Prix 15 is the ultimate speedway simulator of all time. Produced under license by BSI Speedway Limited it brings real sport into video game. Show your skill and tactics in the fight for the title of World Champion in all events and stadiums of the Grand Prix 2015 season!

Tai Woffinden, Nicki Pedersen, Jaroslaw Hampel, Chris Holder… In FIM Speedway Grand Prix 15 you will find all the speedway stars from the current season and real Grand Prix stadiums with different surface types. Powerful, loud engines, high speed, tight shoulder-to-shoulder racing, cheering crowds, clouds of shale and dirt will accompany your road to victory in Grand Prix events - from Melbourne, through Cardiff, to Målilla in Sweden.

Buy and repair motorcycle parts, change settings, on the track search for paths with better grip to gain an advantage over your opponents. Dynamic real time commentary by Nigel Pearson and online multiplayer for up to 4 players!
GAME FEATURES
- HIGHLY DETAILED REAL GRAND PRIX STADIUMS WITH DIFFERENT SURFACE TYPES- DRIVING PHYSICS INCORPORATING CHANGES IN THE TRACK SURFACE
- MOTORCYCLE TUNING AND PARTS PURCHASE, WHICH AFFECTS PERFORMANCE ON THE TRACK
- PROFESSIONAL LIVE COMMENTARY BY NIGEL PEARSON
- TWO DRIVING MODES: ARCADE AND SIMULATION
- ONLINE MULTIPLAYER RACING FOR UP TO 4 PLAYERS SIMULTANEOUSLY!

Enjoy!