The first wing is free. So 2800 gold is needed only. With which you can buy 28 packs, but I think that the adventure is more valuable. You will have fun playing it and there are some fine rewards and if the legendary which will be golden is disenchantable its 100 times worth it.
How do you know it will be fun?
Because if you didn't have fun during the first wing then you wouldn't even be considering this and would be just moving to packs.
So we should assume that you had fun during the free wing and want to know if it's a good value to buy the rest.