The latest Bitcoin miner on the market is currently the Antminer S9. You’ll want at least one of those. Ebay or Amazon is the best way to go.
Use all the listings on Amazon and Ebay to get an understanding of the current average market value. On Ebay focus on buy it now listings. Pay attention to whether or not a power supply is included. If it is not included Parallel Mining is your best bet for a newly crafted PSU available for 110 or 220. Find something for a fair price based on market values. No reason not to buy new at current market prices as of 12/7/2018. Most scammers are looking for a quick turnaround so avoid cheap buy it now prices or listings that look to good to be true because they probably are.
Choosing a Power Supply (110 or 220)
Setting up a Bitcoin Mine