I am using a professional edition. I have a field Matching_Records__c on Lead object which I want to get populated with a link which would contain matching records to that specific record on the basis of some fields ( like Required_Type__c or Required_Price__c on Lead Object) . The query needs to be done on other object records ( LikeType__c and Price__c on Product__c Object). 
What are the approaches I can follow in this case when I can't use any apex?   

I have to follow a specific hierarchy to insert response from external app in salesforce objects. The hierarchy is like- Projects --> tasklists --> tasks. For storing task's project-id, I have to check if the same project already exists or not. If not,create one before creating task. How can I make a comparision between existing records and external app response?