A stroller is fun and but car seats are necessities and $120 will get you a very nice one. We use our car seats a few times a WEEK. It's easier to take them with because they behave themselves (for the most part) in their seats, and it's a million times easier when I am driving by myself (esp. with 2 dogs!). Anyway, I would suggest either a Snoozer Lookout (get the big one) or a Snoozer 3 in 1 (that's what we have - I just use the bottom part in the car.)
Amazon.com: Snoozer Oversized Pet Car Seat... Amazon.com: Snoozer Travelon 3 in 1 Pet Car Seat:...