Lighweight summer bag/quilt

$175 for an EE Rev 50* bag is pretty darn good for what you get.
You get high quality fabric and the ability to fully unzip and just lay it over you.

You may be able to find a used one here?

Hey Jim,

I also sent you a PM for another option.

My wife will be walking the Camino de Santiago route across Spain this summer, and I'm looking for a summer sleeping bag for her. So far the Sea to Summit Traveller TRL bag(50F/10C) looks promising, but I haven't pulled the trigger yet and if there are other, better ideas out there I'm interested in hearing about them.

I work for Enlightened Equipment, so there's that disclaimer, but I will just mention that we've had a lot of bikepackers picking up our quilts this year (which is kind of fun, since I hadn't even heard the term "bikepacking" until this year). A 50° quilt from almost anybody will pack super small though.

It's tough to beat a tiny 50 degree quilt for your purposes. EE and HammockGear are two folks that do a fine job of these. I have a 50 degree summer quilt from one of these companies, and a 40 degree shoulder season (southeast) quilt from the other and love 'em both.

Rei carries 55 degree travel/hostel bags. The synthetic one is very inexpensive. The down one much nicer,and still priced very reasonable ($50-65 if I recall correctly).
Both have a big following as summer bags with the backpacking and river guides operating in the northern virginia area. Both can be zipped open to use as a quilt when it's hot, or used as a bag when it's chillier.

Ps: I'm sure the backpacking quilts are much nicer and pack smaller – but you asked about less expensive options. And packed size probably isn't a big deal. The down one is about the size of a nalgene even though it's a full bag.

Anyone used the silk or coolmax liner bags as standlone summer solution?
Worried it might not be enough to do much

Sounds like a 50 quilt will be perfect for you. At those temp ratings the difference between down and synthetic is not that great so you might also consider an apex filled one from EE for example. Although, if you are really strapped for space while on your bike I guess the down is still that last bit smaller and lighter.

I don't think a liner will add that much warmth, but it might make sleep better, (I know I like sheets even if it is blazing hot in the night). I'm now considering just a bug bivy or bug inner, with my clothes – perhaps bring a puffy jacket for when it does cool down. But I'm talking about 15~20˚C (60~70F).