As stated by several others here, it's basically impossible to recommend a sleeping bag until we know a lot more about how you're going to use it. Where will you be backpacking? Will you be going to places like the Rockies, where it can snow in midsummer? Minimum possible low temperatures? (10*? 20*? 30*? All are "below freezing" and can be encountered in shoulder season somewhere.) Are you male or female (most of us females need more warmth)? What kind of shelter do you use? What kind of sleeping pad? Are you skinny or stout? Tall or short? The bag needs to fit you properly so that you don't press its sides and thus compress its insulation--including when you're wearing insulating clothing--but you also don't want to have a lot of extra air space to warm up. How do you sleep? Do you toss and turn or do you stay on your back all night? All these are important factors in chosing a sleeping bag.

Searching on this forum and in the archives will aid your research. There's a "sticky" post in the General Discussion forum on how to search.

Here are the main top quality brands: Western Mountaineering, Feathered Friends, Nunatak, Valandre, Marmot (their series of bags named after lightweight elements), Montbell. These all have 800+ down fill (search the archives for what this means). A number of these should be within your budget. I have undoubtedly omitted someone's favorite sleeping bag manufacturer; I hope those folks will add them!

EDIT: I missed the statement from the OP that he/she is a hammock person. Heed the recommendations of the hammock folks for a quilt (or two) rather than a sleeping bag, and note the manufacturers they recommend.