Q1:  How much on avg do patents cost?
Preliminary filings can cost up to $12k for the patent drafting and fees, but you should check with your legal counsel. Some offer reduced rates by enabling you to draft and build your application yourself. It takes years to get granted and then enforcement is the real expense.

Q2: How long does the patent application process take?
Depending on your strategy, what jurisdictions you need protection in and the field of your invention, the process can take up to 5 years or more before you can say your invention is “patented”.  If your goal is “value” creation, working with your team and legal counsel you will identify steps in the process that serve as value milestones.

Q3: How much would the enforcement cost on avg?  
It depends, here too there are many stages including identifying infringers, notification, follow-up and then possibly legal action.  As a general rule you should expect enforcement is in the range of hundreds of thousands of dollars while actually getting a patent application granted is in the tens of thousands.