A cheap light meter is the Polaris 2. IIRC, it comes with a 10/18 degree spot attachment. Check out with Ruby on it's price, should be below $300. I won't vouch for its accuracy though and breakdown tendency is high.
A good and accurate light meter is not cheap IMHO. You can consider the Sekonic L308 or the Minolta Flashmeter Vf. I think CP is selling it at $530.