Offensive Security is the most reputable company. These guys invented Kali Linux, Back Track, and the Exploit-DB. Their training classes are some of the best quality material, but are designed for advanced pen testers. There are many detailed guides out there on individuals experience so I will cover the basics.
Meat and Potatoes
The Penetration testing with Kali Linux is the course for the Offensive Security Certified Professional exam. The cost structure is based off of how much time you want to complete the labs, and you can purchase extra time if you run out. The course, exam, and lab time starts at $800 for 30 days, $1000 for 60 days, and $1150 for 90 days. You can purchase exam retakes for $60 each, and lab extensions can be purchased in 15 day increments: 15 – $150, 30 – $250, 60 – $450, 90 – $600.
Kids don’t try this at home
If you are new to pen testing, hacking, coding, etc. do not try the Penetration testing With Kali course or the OSCP exam. It is difficult. It is the industry standard for good hackers. Personally, I am going to get other easier certifications first. It is important to work on learning all aspects of pen testing first. This certification is respected and they want to keep it that way.
There are many people who do write-ups
I will link some of the OSCP write-ups here for you to decide if you are ready or not.