I have not ordered either of these particular items, but have ordered other fabric from this company before and always been very pleased with both the quality and the prices. They are priced by the 1/2 yd.
https://www.etsy.com/listing/510218878/muslin-mates-white-on-off-white-cotton?ga_search_query=white&ref=shop_items_search_127&pro=1
https://www.etsy.com/listing/5384249...search_4&pro=1
Here is a piece of white on ecru from a another good source that I have been happy with. It is 108" wide and has free shipping.
https://www.ebay.com/itm/1-yd-30-Ton...IAAOSwHX5d9-GP
This gal has a lot of white on white options that you might want to consider for later as it is more expensive than what you say you want to spend now. She offers $2.00 shipping if you order more than I item, she only carries high quality, has great service, and is really great to work with.
https://www.ebay.com/sme/shirbrew/2-...white+on+white
Hopefully these suggestions will give you a new source or two.