the raspberry pi 2 & 3 have 4 usb ports, ethernet and hdmi but the 3 has onboard wifi as well.
you'd be looking at buying it from ebay, easiest. $60 - $70 ish for the board. if you want a bundle with case, sd card, cables etc.. thats about $100+
the plus side of a bundled package is sometimes they flash the sd card with raspbian (debian for raspberry pi) but thats easy as fuck to do.
cases for the pi are like $10 and sd cards are like $15 for a 16gb.