As per fourbore's post, those modified in the states have a new (local) barrel, a sling swivel on the barrel, new stock, recoil reducer in the stock and are bedded - that's why they cost more. Typically the raw Czech units were in 375H&H, 416R and 458WM (although when they hit American shores they ran a reamer in these to create 458Lott, hence the double stamping on these ie 458WM/458Lott) - 458WM is problematic for reliability of feeding and the longer case of the 458Lott seems to fix the issue without magazine/feed rail mods.

The modified units were/are available in 404J, 500J and 505Gibbs.

Even the modified units with the higher cost are good value.