Newegg offers the ECS Mini ITX 1150 Motherboard, model no. H81H3-I, for $42.99. A $10 mail-in rebate cuts the price to $32.99. (Amazon offers it for the same price after a clippable coupon, but is temporarily out of stock.) With free shipping, that's the lowest total price we could find by $36. This motherboard supports Intel Core i7, i5, i3, Pentium, and Celeron processors and memory up to 16GB. It includes two Serial ATA 6Gb/s slots, two USB 3.0 ports, and one mini PCI-E slot.
Update: Specs corrected.