Translation:It's expensive to rent a big car.
A small tip. First I would like to say that 借りる (かりる) is to borrow, to have a loan, to rent and 貸す (かす) is to lend, to loan, to rent out.
Now, note that when I write わたしはペンをかりました。 The り is pointing わたし, so I'm the one "receiving" the ペン.
If I say わたしはペンをかしました 。The し is pointing the opposite of わたし, so I'm the one "giving" the ペン.
"Kariru" is a kami ichidan verb according to traditional Japanese grammar which means that it is an i-stem verb.
("Kami" means "upper" and "ichidan" means "one step." The name refers to the fact that all suffixes are added to a stem on the same line (step) of the kana chart and this is the "i" line (step) which is higher on the chart than "e." the stem vowel for "shimo ichidan" verbs. There are only two types of ichidan verbs, kami ichidan i -stems (e. g., kariru) and shimo ichidan e- stems (e. g., taberu).