EVA foam
EVA foam has some of the most tutorials on how to use and sculpt it for art purposes, so it makes for a great learning foam.
Price
depends on type (but is generally the most cost effective foam)
Foam is a light weight, very accessible form of sculpture that can be done with solid blocks or built up layers of foam. All that is required is a box cutter, foam, and the appropriate glue, and then you can get right to sculptuing
Lots of cosplay props are created from foam so that they are light weight, but people also create traditional sculptures from foam. People also use foam to sculpt a form in which to make patterns off of.
There are plenty of online videos and website with recommendations on how to sculpt with EVA foam.
Because safty is such a concern, it is hard to sculpt for long periods of time. You also need to posses a large ventalated space to prime and paint the sculpture.
The only things that have to be bought is foam, glue, and a knife (paint is optional).
EVA foam has some of the most tutorials on how to use and sculpt it for art purposes, so it makes for a great learning foam.
depends on type (but is generally the most cost effective foam)
Contact Cement is one of the glue types that do not melt foam when appled.
~$3 per fluid oz
Rubber Cement is one of the glue types that do not melt foam when appled.
~$4
Hot glue can also be used for gluing foam pieces, but it is for smaller details due to its low strength.
~$3-$5
(+ additional glue sticks)
Spray paint can be used to prime and color a final foam sculpture. It is also the paint that is least likly to flake off.
~$10
(+ additional glue sticks)
The Hot Glue Gun can be used to apply hot glue and add texture details onto a piece.
~$10
Box Knifes are some of most affordable carving tools for foam because you only need to rebuy blades if one goes dull.
~$4