How many schools in Contra Costa (directly funded) have number of test takers not more than 250?
SELECT COUNT(T1.CDSCode) FROM frpm AS T1 INNER JOIN satscores AS T2 ON T1.CDSCode = T2.cds WHERE T1.`Charter Funding Type` = 'Directly funded' AND T1.`County Name` = 'Contra Costa' AND T2.NumTstTakr <= 250