You can use a mixture of trucks and half tracks. Half tracks are quite expensive. So some trucks may make your force a bit more affordable. Your Pak38 can be pulled by either a half track or truck, but truck is more cost effective. Or for something slightly more unusual you could go for a Kettenkrad or heavy field car, both cheaper options. According to the generic army lists you can also use horse drawn limbers too, but they are slow, but very cheap, 10pts regular. Hope that helps.