This is an investment in a sewing tool that will help take your sewing to the next level. I'm giving sources below for each form, but I encourage you to shop around for the best price at the moment by doing a google search on the form/s that appeal to you.
It's hard to give a recommendation, because everyone's body is so different, so just read the descriptions carefully below and you should get a sense of what form is best for your body type.
Here are customizable forms which can be purchased online:
The Uniquely You ($130-230) forms are pinnable, adjustable, steamable on a tripod base; rotating. Soft body form is made of squishy foam rubber that's compressed to fit inside a zip-on cover the user has adjusted to her own measurements; size can be changed by refitting or replacing the cover. Completely unbreakable.
Available here and here
The Fabulous Fit "Maxima" ($337) is a pinnable adjustable form with foam pads, steamable on a four-claw base with casters; rotating. Fitting System comprises foam pads you insert under a tight fitting cover to duplicate your size and shape. Pads can be moved or changed as your body changes.
My Twin Dressforms ($170) are pinnable, not adjustable, steamable on a height-adjustable oak base; rotating. This custom made dress form is a perfect replica of the user's body. It's made by pouring liquid polyurethane expanding foam into a plaster mold that's been formed around the user's body. Comes with a tight-fitting knit fabric cover. If you want an EXACT replica of your body and your body stays around the same size this is a great form. You'll need a buddy to help with the plaster mold process.
There are several sites that discuss duct-tape, papier-mache, and paper tape forms. These will not end up being very easy to pin into which is NOT ideal for the techniques in this class.
Here are some dial-adjust forms that can be purchased at a fabric store chain and/or online. With a dial-adjust form, it's best for draping custom patterns if the form isn't maxed out to the largest size. Get the one that comes closest to your measurements in the closed unadjusted state.
Dressmakers Fit Dressform ($120-150) is a rigid, fabric covered plastic with a pinnable cover. Easy to read adjustable dials at neck, bust , waist and hips. Chalk hem marker on stand, pin cushion at the neck, tripod base. Has a bit more curves in the bust and hip than the Dritz My Double and Twin-Fit models.
Dritz My Double ($130-175) is rigid, fabric-covered plastic with a pinnable cover; 10-12 adjustment dials for circumference; back-waist length adjustments on petite and full-figure models;steamable;tripod base with hem marker; rotating. Available at Hancock or JoAnn's.
Dritz My Double Deluxe ($135-170) is rigid, fabric-covered plastic with a pinnable cover, 12 size adjustment dials for circumference and back-waist length measurements; tripod base with hem marker; extendedshoulders,rotating. Off-center pole option and shaped bottom and thighs for fitting pants. A more realistically shaped hip and seat. A longer support pole for taller women. Available at JoAnn's.
Dritz Twin-Fit ($140-175) is rigid; fabric-covered plastic with a pinnable cover/ 10-12 adjustment dials for circumference; back-waist length adjustments on petite, large, and full-figure models; plastic, tripod-style base with hem marker; rotating. Available at Hancock or JoAnn's.
Here are some forms in a store on eBay--they have many of the styles I've discussed above. There are used forms also on eBay and some great deals, but make sure you check the shipping costs and seller's feedback rating when buying anything online/on eBay.