Here is what I think you should build sometime in 2017. It will still be fairly cheap and will last 5 times longer than the current AM3+ build you are tginking about:
Mobo: AM4 Zen board, go cheap but be sure to get 2 PCI-E x16 slots for upgradeability, USB 3.1 slot recommended along with support for overclocking CPU and RAM. I would estimate $100-$125
CPU: AMD Zen 4 Core/8 Thread (supposed to start around $120)
RAM: DDR4 2800-3000 MHz RAM (1 x 8 GB stick so you can upgrade and utilize dual channel when ready, should cost ~$50 each stick)
GPU: Used 6 or 7 series Nvidia GTX (I got my EVGA FTW 670 GTX for $50) for now until Vega 10 comes.
Drives: 240GB SSD ($50) plus a 1TB mechanical backup (Optional)
PSU: Now everything has been cheap so far, but this shouldnt be. You should get a quality 800+ watt PSU for overclocking ability and upgradeability without having to worry about needing a newer, more powerful one. Raidmax Vampire 800 can be had for around $100.
CPU Cooler: Hyper 212X (New Gen 212 Evo) or cheap 240mm CLC liquid system if you really want to overclock, 212X is $35, a decent but fairly cheap Enermax 240 CLC is $80
Case: Entirely up to you, but I would choose any case designed for up to E-ATX boards in case you want to change it later (ATX Full-Tower). Decent one can be had for about $60, but I just got my Cougar Panzer Max today. Yea its $150, but boy was she worth it. Can support up to two 360mm radiators AND a 120mm AND a 140mm, or 8 fans. Basically, unlimited upgradability for life. I dont think I will ever buy another tower lol. Looks pretty sick too.
So depending on how you go about it, you could build an entirely brand new PC with the latest Zen Technology by mid 2017 for about $600 (not including OS), and then instead of buying a new PC later, throw in a second stick of RAM, the CLC cooler, Vega 10 card, overclock that CPU to its max, and you should be pretty on par with an Intel i5 Skylake system with a GTX 10 series. All for about $1000 even. Enjoy.