Learn Dutch: Ik zou de hondenmand kopen, mits hij goedkoop is. - I would buy the dog bed, provided that it is cheap.

Hondenmand is a compound noun made of hond (dog) and mand (basket/bed). The rule for the linking -en- (often called the tussen-n) is that if the first noun has a plural that ends only in -en (like honden), you use -en- to glue the words together.

I don't see mits very often. How does it work here?

Mits is a conjunction that means "provided that" or "on the condition that." It introduces a dependent clause, which is why it kicks the verb to the very end of the sentence, giving us mits hij goedkoop is.

Why use hij (he) to refer to a dog bed?

Because mand is a de-word (de hondenmand). In written and formal Dutch, you use hij to refer back to singular de-words, even if they are inanimate objects. You would only use het (it) to refer back to het-words.

Why is kopen placed at the end of the first clause?