If you don’t have a lot of money to invest in employees and you’d rather work on your domain portfolio by yourself, you’d need plenty of free time. Generally, mini sites with 5 to 10 pages of content can be built within 5 days, while authority sites with over 10 pages could take up to two weeks. This amount of time would depend on your writing skills and knowledge of SEO techniques.
One of the best ways to obtain a valuable domain that is already search engine optimized is to purchase existing domains via auction sites.  This strategy can be beneficial mainly in two ways.  Firstly, any domain that has already been purchased was probably already researched for potential benefits.  Secondly and more importantly, the second benefit is that many recently expired domains still retain some of the search engine optimization attributes that were built up by the previous owner. For example, a recently expired domain name may still have active backlinks on the web, and the page rank of the domain could still be high, giving the purchaser instant SEO gratification with minimal effort.
In theory, you could technically acquire a domain for $10,000 and be able to sell it for $100,000. You could also acquire a domain for $10 and be able to sell it for $100,000, $10,000… or $100, you get the picture. Because of this, it’s hard to recommend a perfect starting budget because your strategy, experience, and the pace at which you learn will hugely affect your buying and selling decisions.