While I love the Litko stuff, and have bought some miscellaneous stuff from them, I'm still an "old timer" when it comes to figure bases.
If I'm doing multiple-figure bases without singles for casualties or skirmishing, I use artist's illustration board from a store like Michaels or Hobby Lobby. It is a laminated product that usually has either a gray or a greenish-blue back and a coated matte white surface finish. It takes all adhesives and paints and doesn't warp unless you really load it up with wet putty or spackle. You can cut it with a craft knife or a hinged-blade type paper cutter. I then put self-adhesive magnetic sheet on the bottom when I've finished my base texturing and line my carrying cases or boxes with thin galvanized roof flashing available from DIY stores like Lowe's or Home Depot (can be cut with heavy-duty scissors or tin snips).
You can do a Litko-style base, if you're willing to do a bit of extra work. Base your figures on inexpensive 1" fender washers (again, Lowe's or Home Depot) and terrain the washers when you're done painting. In the meantime, lay out some washers on a piece of the illustration board to determine your size and shape (squared-off or irregular like a Litko "Horde" base) and trace around the washers with a pencil. Cut the illustration board with heavy scissors or a craft knife and then use some epoxy putty or thick spackle and build-up the edge of the base and the spaces between the washer patterns. When your filler is dry, paint the base and flock or sand just the built-up parts. If you're work is neat, your washer-based figures should drop right into place.You can even cut some magnetic sheet into circles and put that into the "holes" so that your washers are held in place.
While round bases seem to be the "rage" right now for skirmishing, role-playing and such, you can also get 1" square galvanized metal bases made by Wargames Accessories through folks like the War Store or Grandiosity (warweb.com) very reasonably. It makes your "trays" easier to cut out and you only have to build-up the outer edge of the tray, not the spaces in between. It makes cutting the magnetic sheet much easier too. Also, speaking of magnetic sheet, while you can get about a 9 X 12 sheet at Michaels or Hobby Lobby, if you have a local sign shop (and almost everyone does now-a-days), they usually stock this material in 12", 18" and 24" wide rolls. They will usually sell you this stuff by either the inch or the foot. A friend of mine does so many figures that he found an online source and just bought his own roll.
Hope this is of use, just some rambling tips from an old-timer.