I think it's one of those things where you are either an animal person or you are not.
I am. I've always (until recently) worked with animals, and because I was working full time with them my collection was limited to hamsters and fish. I wasn't around to look after anything else properly and I had my 'fix' at work.
Now, I am at home full time and I have a dog. I'd go mad without animal contact - it is just part of who I am.
We don't have much money, but then neither of us smoke, I don't drink alcohol and DH only has a four pack of beers every couple of months, and we don't go out to eat, ever - the last take away we had even was over a year ago, so I'm guessing we spend quite a bit less than others would spend on those sorts of luxuries. In fact, I mostly drink squash or water. I don't even splash out on coke or other fizzy drinks!!
I'd rather do that, it's no big deal, and have enough left to pay for dog food and insurance than drink 'nicer' drinks, or get take aways on a regular basis, and not have the dog around.
I'd also quite happily give up the TV before giving up the dog, if it came to it.
If you are not really that bothered about animals, you will never understand.
We went away for six weeks over Christmas, to see DH's family overseas. I missed my dog with a physical ache by the end of it. It is part of a lifestyle choice - the walking etc is all part of the enjoyment for me, rather than a responsibility and a chore, but I also find that after a few days of no animal contact I start to almost crave the feel of their fur under my hand, or the joy I get watching and playing with them, or the peace they can bring. You will either understand and 'get' that animals are more than a luxury sometimes, or you won't.