Bsically all the plastic materials should fit your basic requirements. It depends on what you call "Medium detail"
WSF (or Black SF) is cheapest. You should be able to get minis at prices comparable to comemrcial 28mm figures. The surface is rather rough and you will have to prime it heavily because it absorbs paint like kitchen paper would.
Detail (White, Black, transparent) is more expensive, but has better detail, and is more easily painted.
FUD is most expensive, but has the best detail.
Check out the forums for the drawbacks and advantages of the materials and how to treat them. Also a number of shops have 28mm miniatures, often with photos of finished minis. Check them out. Prices can be comparable to 28mm from commercial manufacturers using metal.
Greetings
Dragoman