The dress form I own is the "Uniquely You" a customizable dress form which is made of a high density foam which you customize with a canvas cover that has been altered to meet your measurements. The dress form comes with a cover but additional covers can be purchased to accommodate weight changes or multiple individuals (provided you are roughly the same body size).
Now this dress form is obviously not homemade, but it takes quite a bit more work than your average "dial a size" form. See the (hilariously old-timey) instructions:
There are two main challenges to fitting your dress form. First, you have to perfectly fit your canvas cover. This can be a bit of a struggle, particularly if you don't have a friend on hand to help you out. Working alone this took me several hours of sitting alone in front of my sewing machine in my underpants. I would turn the cover inside out, put it on, pin, stitch, and repeat making tiny adjustments until it fit like a second skin. Which leads us to the second challenge... to assure that the canvas cover is properly filled out, the underlying foam form is significantly larger than the final intended measurements. This means that you may break a bit of a sweat wrestling some laughably enormous foam bosoms into your canvas. However, once the canvas is zipped up and the foam appropriately compressed, it creates a dense, pinnable form that should closely mimic your figure.
The form comes in 5 size groups with 14 adjustable cover sizes.
Now it's been over six years since I purchased my form, but I believe I bought a medium form with a size 9 cover? Due to some weight gain in the ensuing years, if I was to buy one today I would probably get the medium large with a size 11 cover, but I'm working on that!
A few thoughts about this form that you may want to consider... I love this form but I am not that far off from a "standard" figure. I tend to be a bit bustier than average and sport some junk in the trunk as it were, but my measurements generally adhere pretty closely to those propogated by the Big 4 pattern companies. I don't know how much my love of and success with this form is related to the relatively minor adjustments that I needed to make. Also, I am uncertain as to the compressabiliity of the shoulders and back width. One thing I LOVE about my form is that the shoulders are perfectly my size (even with the weight gain) which makes it much easier to install sleeve caps and so forth. However, I have fairly balanced and squared off shoulders. If you have a severe slope or narrower shoulder and back it may or may not work for you.
Finally, as for price... Now this is obviously not going to be as cheap as the DIY dress forms made of duct tape, paper mache or the like. That said, it is not unreasonable compared to other options on the market. Various sites price this out at between $139.99 and $189.99. Given the advantages (no sticky residue on your pins! practically industructible!) I think the price is well worth it. And keep in mind, when I decided the price was worth it, I was on a student budget... As an adult with a grown-up job my reaction is "OMG BUY IT! BUY IT! SOOOOOOO worth the cost!"
So there you go, more than you ever wanted to know about my dress form. If you are interested in getting one for yourself, here are the resources I found:
Allbrands (this site looks familiar and I think this is where I ordered mine lo these many moons ago)