We can put a campaign together that works with whatever budget you have available.

Instead of asking "How much should my PPC budget be?", you should be asking, "How much money do I have available to spend on PPC?"

Generally speaking, the more money you are able to spend, the better your quality score, ROI, click-through & conversion rates. 

Minimum budget required to start PPC services is $300/month. However, you generally want to spend much more than that, particularly in urban areas.