Well, in 3 months, these prices are going to be wildly inaccurate so you may not be able to get the same build. But if I were going to build a PC in that budget with upgradability in mind, here's what I'd do:
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Core i5-6500 3.2GHz Quad-Core Processor | $204.99 @ Amazon |
| Motherboard | ASRock Z170M Pro4S Micro ATX LGA1151 Motherboard | $98.99 @ SuperBiiz |
| Memory | G.Skill Ripjaws 4 series 8GB (2 x 4GB) DDR4-2400 Memory | $53.99 @ Newegg |
| Storage | Samsung 850 EVO-Series 120GB 2.5" Solid State Drive | $65.49 @ OutletPC |
| Storage | Hitachi Deskstar 1TB 3.5" 7200RPM Internal Hard Drive | $39.70 @ Amazon |
| Video Card | Gigabyte Radeon R9 390 8GB SOC Video Card | $263.99 @ Newegg |
| Case | Enermax OSTROG ATX Mid Tower Case | $39.99 @ Newegg |
| Power Supply | EVGA 500W 80+ Certified ATX Power Supply | $34.99 @ NCIX US |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total (before mail-in rebates) | $842.13 | |
| Mail-in rebates | -$40.00 | |
| Total | $802.13 | |
| Generated by PCPartPicker 2015-10-05 13:31 EDT-0400 |
On the Skylake socket with DDR4 RAM and a DX12-ready GPU that'll destroy games at 1080p. Got an SSD for a boot disk and a 1tb HDD for storage.
As for the case, you can switch it out for whatever works for you, that one is cheap, nice features, and has good reviews. I use a slightly larger version of that case which I've loved so far (not the prettiest case but it's got plenty of nice features), but it's largely a matter of taste so pick whatever you want, PCPartpicker automatically filters out incompatible cases and warns you if there's any problem with, say, the GPU fitting inside the case.