Moosejaw offers the Marmot Men's Mavericks 40 Semi Rec Sleeping Bag in Fire Red for $52.99. Coupon code "MRREB5" cuts it to $50.34. With free shipping, that's the lowest total price we could find by $7. It's available in regular size with a left side zip.
It's also available in long size with a left side zip for $54.14 with free shipping after the above code.