$300 budget. Down bag. +30-40 degree.

RE: side sleeping w/ a quilt,

I am a side sleeper and use a Katabatic Gear Palisade without any strap system and it works great. You just have to remember to keep it tucked. If you sleep under a tarp or open shelter, a bivy would help a lot.

i use a warbonnet black mamba long/wide for hammock use, but i'd be totally confident in that extra material being plenty for ground sleeping. in the hammock it just piles up on top of me into warmy goodness.

http://www.warbonnetoutdoors.com/topquilt.php

I find the Mountain Hardware Phantom 45 to be a nice bag. It is warmer than my 32F rated bag. It is very conservatively rated IMO and I have found it comfy down to 30 or so without supplemental clothing. It is in your price range and might work out if it is warm enough for you.

Another vote for the stoic somnus.

You can find them on gear trade for $100 if you wait around long enough.

I am not a quilt guy but I have read nothing but rave reviews.

http://enlightenedequipment.com/index.html

Get a Hydrogen on sale or at REI with a 20% coupon and you are at $300 or better.

Feathered Frends' 30 degree bags are just over $300, if you can swing a little more.

FYI, I'm not a quilt person.