The first thing to do is check junkyards for used seats. The 240 series seats hold up quite well, so finding decent ones may not be difficult.
There are pieces available to rebuild the seats (foam, the metal grid on the bottom, and the lumbar), but it's expensive. For the price of the foam alone from IPD, you could probably buy several pairs of junkyard seats.
If the junkyards have been picked over, chances are that torn vinyl 240 seats will be left behind. This may be a good source for replacement foam for your seats.
I got a pair of decent tan vinyl seats for free from someone just looking to get rid of them. If you have tan seats, I can give you the cover off of a tan vinyl seat for the cost of shipping. I think it has a couple of small tears, but it's not split or cracked. It could be used on the drivers side instead, but there would still be a hole on the right side from the lumbar adjuster.
Here's a page that describes the replacement of seat foam:
There are also covers available that go right over the seats, but these are really only good for seats with solid foam and worn fabric/vinyl/leather.