Simplify the following text for a Grade 9 native English-speaking person.
Original: They can be inexpensive : some variants can cost as little as US$ 1000 , though more sophisticated mines can cost millions of dollars , be equipped with several kinds of sensors , and deliver a warhead by rocket or torpedo .
Simplified: There are very advanced mines which can cost millions and have several kinds of sensors , and deliver a warhead by rocket or torpedo .