I would translate it as: This car is expensive but I didn’t buy it. But it makes no sense.
I hope you can explain how to translate this sentense properly step by step.

つこみさんのほん = Tsukomi’s Book OR the Book of Tsukomi.

ちいさいはなのいもうと = The small nose of my sister, or The small flower’s sister. (For those who don’t know, はな means both nose and flower)
It’s really quite confusing when you think about it.

I also wanted to comment on the Kau/Kaeru thing.
Whats funny is that Kaeru can mean Frog, to return and is the “can” form of buy. There is no real term for WON’T BUY because WON’T is a future tense (it makes more sense when you de-contract it, will not) and Japanese doesn’t have a definite future tense. Doesn’t and Won’t are the same thing Kau. Kaeru means you CAN buy it. (and of course it also means from and to return)

You cannot use “Ie ni konai mo ii” although most Japanese understands what it means but not proper.

Thanks alot!