How much would it cost to redo my 8 porcelain veneers? (Photo)

Save a lot of money, worry that the result looks fake. A good job will average $13,000 to $20,000A less than satisfying result is often from not doing enough teeth, or the color is monochromatic (one color instead of blended shades). 

A few questions first will help:
1) Why do you want or need them replaced?  Do you just not like the shape, shade or thickness or are they leaking and getting stain around the edges or decay?   Damage occurring to your teeth could result in more dental work or simply doing a all ceramic crown for strength verses just the front of a crown which is a veneer.  Ceramic Crowns can be similar or less expense and have better fit.....but would have to remove more natural tooth structure.  
2) Make sure you communicate exactly what you want as a result and what you would do differently from these existing veneers to your dentist.  Veneers are like vinyl siding, a durable cosmetic front surface which covers part of the tooth and leaves the back side exposed relying on bonding (glue/cement) strength verses mechanical fit. 
3) Protect your investment;  Your dentist will likely evaluate any para functional habits like night time tooth grinding or clinching as well as suggest a sleep bruxism/apnea test to see if a night appliance would benefit you by protecting your new veneers.  
4) You may want to just get 3-4 face to face opinions with other dentists if you are unsure and see which ones educate you the most on your situation, take photos and offer the best solutions to your situation which may or may not involve 8 veneers.

There are different factors that determine the aesthetics of the veneers. The type of the porcelain, the skill of the master ceramist, the skill and experience of the dentist preparing and cementing the veneers, the shade of the teeth under the veneers, and your bite all determine the quality and outcome of a natural, beautiful looking veneer result. In my Scottsdale, AZ office you are looking at $10,000- $12,000 for 8 porcelain veneers with a natural beautiful outcome.