Amaan909 :
raisonjohn :
Cheapest motherboards you can use (under $50): https://pcpartpicker.com/products/motherboard/#c=112,113&f=7&sort=price&page=1&X=0,5093
But all of these are ddr4 but i am lookinf for ddr3. I know ddr4 is better but i already have a ddr3 stick and dont want to spend more money on ram
As of this date, there are only 2 options in pcpartpicker that offer motherboards for your i3-6100 with DDR3/DDR3L support (https://pcpartpicker.com/products/motherboard/#c=112,113&f=7&sort=price&L=3&qq=1) which is the Asus B150M-C D3 ($82.00 @ Amazon) and the Asus B150M-A D3 ($199.89 @ OutletPC).
Note also that those motherboards recommend using DDR3L (low-voltage RAM, lower than 1.5V), so, if you have regular 1.5V DDR3, it would cause system intstability (even potentially damaging the component/s).
I would suggest you get the DDR4 motherboard suggested in my first link (such as the ASRock B150M-HDS being offered at a discounted/promo price of only $46 in Newegg. Then, get a new DDR4-2133 RAM kit for ~$70 (for 8GB capacity).