A Kodak Q-60 slide is about 70 USD and available from Kodak Professional.
There's one problem with a Q-60 slide, you need a load of ancillary gear to use it and it only will tell you how accurate your scanners colour is on a fully colour corrected system. (and accurately corrected at that). That will entail another few grand in hardware and software expenses.
Far better to spend 300-600 bucks on a simple spyder and monitor calibration package.