Hi kss1001,
Welcome to the Mattress Forum!
I’m glad the information here has been helpful to you.
The good news is that you shouldn’t have too much of a problem finding something in that price range for a growing child that meets your guidelines.
You may have read this already but just in case you haven’t, there is more information in post #2 here and the topics it links to about mattresses and children and “suitable” and “safe” materials including a link to some general guidelines for children in post #2 here. It also includes a number of links to the better forum posts and topics about mattress and children as well which have more information about many good options children that would be well worth considering.
As far as a low-VOC certification, CertiPUR-US would be a common polyfoam certification that tests for harmful substances and VOC’s in the polyfoam and memory foam used in mattresses. Here’s a listing of some of the participating companies. Here’s what CertiPUR-US certifies. Mattresses using these certified foams are quite common.
Regarding the flame retardant barrier, most companies are not using chemicals to meet 16 CFR 1632 and 1633. The most common method used to pass the regulations is the use of inherent fire barrier fabrics that are either quilted into the cover or are wrapped around the inner materials of the mattress (like the sock you mentioned). There is more information about fire retardant methods that are commonly used in the industry in post #2 here and in post #4 here. These inherent fabric-type of barriers are ubiquitous in the mattress industry.
Subject to first confirming that any retailer or manufacturer on the list that you wish to visit is completely transparent ( see this article ) and to making sure that any mattress you are considering meets the quality/value guidelines here … the better options or possibilities I’m aware of in and around the Sarasota /Brandenton area is here .
You really shouldn’t have much of an issue finding something within your price range close to home. If you have more specific questions on anything you find, please let me know.
Phoenix