You won't find DDR3 Crossfire board for under ±R2500.
Some models to look at:
DDR3, no Crossfire, R1500 - R2000:
Intel P45SG SkyberG ; intel Quad-core / Core2 / Core2-extreme / Pentium D / Celeron-L (800fsb) , 1333/1066/800fsb , intel P45 + iCH10R chipset , 4x dual channel DDR3-1333 ( support XMP ) upto 16Gb , 5 x s-ata2 + 1x e-SATA with raid 0,1,0+1,10,5 , no parallel ata133 ; on-board gigabit lan + ieee1394a + Intel 7.1 HD audio with optical spdif out ; 3x pci, 2 x pci-e(1x), 2 x pci-e 2.0 (16x / 8X+8X ) , atx , no PS2 - bulk pack.
ASUS P5QC , DDR2+DDR3 , with EPU-6 ( Energy Processing Unit ) ; intel Quad-core / Core2 / Core2-Extreme / Celeron-L (800fsb) / p4 / Pentium D ; intel P45 + iCH10R chipset , 1600/1333/1066/800 fsb , , 4x dual channel ddr2 1066 ( upto 2.5v ) + 2x dual channel DDR3 1333 ( upto 2.2v ) upto 16Gb , 8 x s-ata2 with raid 0/1/0+1/5/10 , 1 x parallel ata133 , on-board ALC1200 7.1 audio with coaxial S/Pdif out + 1394a + gigabit lan ; 2x pci , 3 x pci-e(1x) , 1 x pci-e2.0 (16x).
With DDR3 and Crossfire, R2500 - R3000:
GIGABYTE "S Series" P45 & ICH10R Chipset Socket LGA 775 @ FSB 1600 - For Celeron®D, Pentium®, Pentium®D & Core™2 Duo & Quad
2x 16X PCI-E, 3x PCI Express 1x slots, 2x PCI, 4x DDR3 1600 (Dual) ,6x Sata2 RAID 1x ATA 133, 12x USB 2.0, 2x Realtek GBE LAN
Durability 2 Series - All Solid Capacitors, 8 Ch HD Audio, Gigabyte SPEED, SMART & SAFE, CROSSFIRE, Gigabyte DES Tech, Ultra TPM.
intel X48BT2 BoneTrail 2 , support pci-e 2.0 crossfire ( 16x+16x ) , with on-board on/off switch ; intel Quad-core / Core2 / Core2-extreme / Pentium D , 1600/1333/1066/800fsb , intel X48 + iCH9R chipset , 4x dual channel DDR3-1600 ( support XMP ) , 8 x s-ata2 with raid 0/1//0+1/5/10 ( 6 x internal + 2 x external ) , 1x parallel ata133 ; on-board gigabit lan + ieee1394a + Intel 7.1 Dolby Home Theater Audio with optical spdif out ; 2x pci, 3 x pci-e 16x ( 2 x pci-e 2.0 + 1 x pci-e 1.0 @ 16x+16x+4x ) , atx , no PS2 - bulk pack.