Check on rei or rei outlet and see what's on sale. You can end up spending a lot of money on a sleeping bag, which could then do away with the price of gas... Are you planning on continuing to tour with your bike or hiking? IF that's the case, then you should go ahead and invest in a nicer bag. If this probably a one time thing and you don't have much to spend and it's going to be relatively warm - then don't spend very much on a bag.
It really depends on what you want - a down sleeping bag is going to compress smaller than a quallofill bag - however, a down sleeping bag will not remain warm if it gets wet. A quallofill bag will remain warm when it's wet, but won't be as compressible - and this is a bike trip you're on.
It also depends on what temperatures you will be sleeping in - you can get sleeping bags that are rated to -15 degrees, 15 degrees, 30 degrees, etc.
REI's housebrand of bags tend to be good deals:
http://www.rei.com/outlet/search?sea...2Csleeping+bag
If you're a tall person, you should get the longer length bag. Women's bags are wider in the hips for women's hips - so you might be more comfortable in one of those.
I like the mummy style ones that pull over your head.
I use a marmot helium 15 degree for hiking, and a sierra designs glow for kayak camping.