$2000. If you are lucky.
I am not joking. There is money to be made in domains, sometimes quite a lot of it, but only if you buy the RIGHT domains. Most domainers price their names to sell to end-users. That means someone who is in the business referred to by the domain and who needs that particular name to build their website. Such buyers are very rare, but when they show up they often will pay ten, twenty or more times the price a domain investor (who is interested in a variety of names) will pay.
So if you buy without knowledge you will pay end-user prices when you are trying to invest. The answer is knowledge. It is almost all here in the NP forum - read read read, then read some more. I would not consider spending $20,000 until I had mastered the information on this website, and then would stick to safer areas like LLL.com and LLLL.com.
To directly answer your question, high value domain names historically gain around 40% or 50% per year. But ya gotta do the learnin' before you do the earnin'.