hi..
manufacturers don't normally post the price of the drives esp. on that size....250HP on the web..
you can contact some manufacturers/distributors by phone or by e-mail and give them the specs. of the drives you are interested in..just watch for the price..some are cheaper but with cheap performance too...
Suggestion: There might be some prices available in literature within a technical library to have some idea of variable speed drive prices. Since there are various speed drive principles, the prices will vary accordingly.