Minimum 2400g or 1600. If you can afford graphics card, 2600,1600x,1700 sounds about right. Otherwise 2400g would probably do what's needed and save some money.
Can you recycle your current graphics card and would it be powerful enough? If not, entry cards are around $100 (1030 nvidia, or rx 550) and better ones a little upwards of $150 right now (rx 560).