How can I keep costs to an absolute minimum in the event of a passing off or infringement claim?

Lawyers charge on a time spent basis. Work up a relationship with your lawyer where you are clear about what it is you want your lawyer to do and ask them how long they think a particular task will take. Ask them how much they think something will cost, but also understand that if you want something else undertaken outside of the scope you agreed you will incur further charges. See what aspects of the work you can undertake yourself and what work you require the lawyer to do. Ensure that you gather together all your evidence and examples of copying prior to contacting a lawyer so that you are prepared and do not waste time or cause delays through lack of evidence. The ACID IP databank is a fantastic tool for ensuring you have a stringent audit trail.