If money is no issue then here´s a list with ideas and materials:
1: as mentioned before, start with a sturdy base to work from. Plywood or similar. You can make 4 pieces that slot together for easier storage or stick with one big piece.
2: Styrofoam. Cut pie sections out of 1" thick styrofoam for the banking and check the banking angles. Glue the pie sections to the wooden base along the lines of the racetrack. Space them at 2-4" intervals.
3: track surface. Start with a layer of styrofoam. If you can find 1/2" thick styrofoam, go with that. It´ll follow the curves of the turn better. Best cut sections as large as you are comfortable with, but don´t worry about a perfectly smooth surface yet.
After glueing and fixing it all together take coarse sandpaper to smooth the turns.
You can use the sandpaper to create some wear on the track. If you decide to paint the styrofoam surface the way it comes out after sanding use latex paint and latex paint toner found in DIY stores. You can mix in birdsand to cover some of the unwanted irregularities you got in the foam when sanding it.
If you wish to apply sandpaper as a road surface you can apply a layer of PVA glue on top of the styrofoam instead after sanding it. Glue a layer of the sandpaper of your choice on top of that.
4. For the concrete and safer barriers you can cut strips of the 1/2" styrofoam. For the rounded sections use a wooden or plastic roller (kitchen equipment, ask the wifes permission or make sure she doesn´t find out you used it) and roll them on a hard and smooth surface. Use little pressure, and you´ll see the sections curving a bit. Once they have an initial smooth curvature, just glue them in place and fix them with toothpicks or similar.
5. Catch fence, see Danicafans´ post. That´s a brilliant and simple idea. It works.
6. For the infield and grass sections, first apply the same textured paint you might have already mixed up for the road surface. Best mix in some coarser sand to get a bit of structure. Paint this in green, then apply static grass which you can buy from model stores.
That should give you a good start into the project. I can provide more detailed instructions if you have specific questions