First, focus on what you want your message to be. Who is the intended target of the pitch deck? Brainstorm on the message you want to convey: what's the "pain point" you're solving, what's the market opportunity, number of customers you have, amount of capital you're seeking to raise, why investors should invest with you (your "special sauce").

Once you have all this information, then you can approach various consultants/shops and see what their pricing/track record/etc. is. But looking for a consultant before you know exactly what you want will just waste a lot of your time.