The fabric for my Regency chemisette and fichu were given to me by a friend.
First off, for 1860's things, one can get away with 7 yards of 45" or 6 yards of 60" (though I once got away with 5 yards of 60"... not sure how I did that!) It is very, very, very crucially important to get enough for a dress at once. Fabric often is hit and run. If you think that you can just go back to the store or website and buy more when you can, I'm afraid you'll have many too-small lengths of fabric lying around that you will have nothing to do with! So always buy as much as you need for your entire garment.
I was able to purchase this black silk for $12.50 and this blue silk for $10 because of using 50% off coupons at Joann's
Secondly, Joann's, Hobby Lobby, and Hancock's can be nice and local, but it's very hard to find period-correct cotton prints when you are not shopping with a mentor (which you should always do!). I prefer online retailers because I can email links to people who are much more knowledgeable than me and also post on online forums such as The Sewing Academy. You can also post pictures of fabrics you see in store, but like I said before, fabric stores are a hit and run and you never know if it will still be there when you come back.
This red wool was purchased from Fabric.com during a sale, and cost around $6 a yard.
So, here is a list of my favorite online retailers:
Fabric.com - Good selection of tropical weight wools for dressmaking (my red wool is from Fabric.com), decent selection of reproduction cotton prints
Fashionfabricsclub.com - Every fabric known to man, pretty much. Decent prices and nice fabrics. My lavender semi-sheer plaid is from there, along with my Regency striped fabric and Sarah's blue plaid shirting for her 1860's wash dress.
Fabricmartfabrics.com - Very nice fabrics, good wools, silks, and cotton semi-sheers.
All of these retailers are great, but some of their fabrics are exorbitantly expensive--that is, if you look at the wrong time. Which brings me to my next topic...
The fabric for my 1860's wrapper was purchased from Fabric.com for $3.50 a yard, after posting on the Sewing Academy for approval of the fabric.
Sales, clearances, closeouts, whatever you call it, these are a seamstress's best friend. I rarely ever buy fabric when it's not on sale. Each of the websites I just listed have email lists notifying customers of sales, clearance sections, and even "Dollar Deal" sections (one of the reasons why I love Fabric Mart so much. I bought the most beautiful green and white semi-sheer plaid from there for $1 a yard!) Troll the sales. Sometimes you can score $4 a yard wool or $1 and $2 a yard cottons!
I purchased this medium-weight wool at Fabric Mart for $5 a yard, and the polished cotton and wool batting for $5 and $10 a yard, respectively. Ebay is a good place to find fabrics, but it requires a great deal of wading through improper fabrics. Remember to narrow your search using the sidebar on the left.
And also, COUPONS! Almost every retailer has at least one coupon active at any given time. Websites such as Retailmenot.com and store emails are very helpful in notifying you about coupons. When I got this:
I purchased this fabric from Fashion Fabrics Club for $6 a yard
And finally, and less easily, make reenacting friends. I know many, many people who have large stashes of period correct fabric that they could never completely use in their entire lives (we call that Stash Beyond Life Expectancy). The fabric for my yellow dress was bought from a good friend, Hannah, who had bought it with hopes of making herself a dress. I also bought a dress length of block printed Regency cotton from a lovely woman I met at the Jane Austen festival this year. And, my final steal will be explained in detail in my Perryville post, but I must say it was quite a deal!
I hope this helped and I wish you all safe travels in the abyss of online fabric shopping!