What is the average cost of a pig pen?

Pig pens vary a lot in cost, based on whether you design and build yourself or buy premade. Also, whether you import or not. Looking online, it looks like you can get all the parts to build one (with plans online as well) for about $30 or so (new lumber). The pre-made ones I am looking at start at a comparable price (but are imports and would probably cost a lot for shipping) and go up to about $120.