I have a purebred Shih-Tzu and a dog from the pound that was later "diagnosed" by the vet as a Shih-Tzu/Lhasa Apso mix. Nice thing about Shih-Tzus is that they don't shed everywhere. However, this tends to lead to mats in the fur on their ears and their tails. The purebred is cute, very nice to family, healthy, and stupid. The mix is cute, very nice to everyone, smart, and has numerous health problems. Both are inside dogs, but are fine outside. I'd say they'd cost around $15 each per week. They'd cost even less if I cut their fur myself. After each haircut, they take about 6 weeks for their fur to grow back out to
this length. The mix only required minimal training. I groom their fur about once a week at most, usually. They don't really require much exercise. They're small bot not "toy"-sized like a chihuahua.
But [PRO-TIP]: Don't have the dog get used to using pads as their means of a restroom. The breeder did this with the purebred, so I just kept doing it. But then he started associating that with everything that was on the floor (including towels and beds). He poops and pees on almost anything now if I don't take him out in time.
A cousin of mine has Border Terriers. 3 of 'em. 2 males and 1 female. One of the males is smart like my adopted mix. The other is not too bright like my purebred. I haven't been around the female very much (she's only about a year old), but she seems to be the most aggressive of the bunch. She's also the smallest. Their coats are pretty wiry but short. The males are a bit bigger than my dogs, but not by much. Not sure about much else. =X
I'd suggest looking at websites that have information on many different breeds.