Over the years I have accumulated a bunch of crates of all sizes. And with two exceptions I bought them all at yard sales and they were dirt cheap--small ones as little as $5 and big ones maybe $20. Which doesn't solve your immediate problem. The one I actually bought at retail and use for all small puppies was a 300 VariKennel. Most of the time it lives as a spacer in the canopy with a 400 VariKennel--but even my biggest dogs can (and will voluntarily choose to get in that one).
And you can block off part of bigger crates (the wire crates often have a moveable divider to use) for smaller puppies.
A 400/Large size (36") crate should fit in your SUV without a problem. If you get one smaller, the puppy will outgrow it in no time. This size crate will fit a female for travelling their whole life. A male will likely need a 500/XL (40-42") when grown, but it may or may not fit in your SUV.
In Rottweilers a 36" crate is sometimes referred to as a "bitch crate," and a lot of people use them at shows and in cars. I don't know if they also use them at home, but for me 36" seemed too small to be really comfortable, and I used a 42" for my females, who all weighed about 85 pounds.
Like dobebug I have a variety of crate sizes. Have never used a divider, and I'm probably wrong to find reasons to worry about such a thing, but I do. Gibbs the German Pinscher was close to Doberman size as a puppy -- 20 pounds when I got him at 11 weeks. He started in a 24", which was big enough for him and his Cuddle Puppy, and went through a 30 and 36. He's now in one of the 42s I had for the Rotties. He is oversized for a GP at 52-54 pounds, and if he stretches out he can use all that length, but he can also curl up and make it look ridiculously too big. That's fine with me as I want my adults to be able to stretch out comfortably in their crate. For that matter I don't squash puppies as tightly in a crate for housebreaking as I often see recommended.
You can use a couple of plastic file boxes taped top to top to block off the end of a large crate to make it puppy sized--which is really necessary at first to help you potty train the little tyke. They generally won't mess their beds, but if they have room to get off the bed and squat, they will.
I was lucky to find a brand new never used JEEP soft sided one on Facebook marketplace for $40 CDN. It was perfect with room to spare. I had a big fluffy bed in it too. The kennel measures 31" x 22" x 22".
Here is a link for visual reference.
Keeping pets while in the Jeep has never been easier with the Pet Kennel by Mopar! This collapsible kennel is made out of strong nylon mesh material and includes two storage pockets, three door openings, and a carrying handle.