Many kids ride rear facing in one car and forward in another without a problem. I bet she's not eager, but many parents think their kids are.
Two is the absolute bare minimum to be forward facing. I wouldn't forward face her even occasionally in other cars. At her age it's up to 534% safer to rear face. Hardly a trivial amount. Rear facing is safer for EVERYONE, but under two is absolutely vital, and most of us rear face to our kids to at last three to four years old. Hence the recommendations for you for a rear facing seat, rather than a forward facing one. Rear facing as long as possible does not mean until two. Rear facing as long as possible would mean taking a small child to close to *six* years old.
So, for a 17 month old who needs another seat, in the $100-$150 range, looking for less bulk side to side, I'd look at the Graco My Ride and Safety 1st Complete Air. They both rear face to 40 pounds The Complete Air is taller and so will last longer rear facing by height.
The My Ride is easy to find under $150. The Complete Air I'm seeing several online, but not sure if they'd be in stores in that price.
http://www.toysrus.com/product/index.jsp?productId=4232164&CAWELAID=602137697 http://www.samsclub.com/sams/shop/p...CSE_Froogle&ci_src=14110944&ci_sku=sku5334072 http://www.toysrus.com/product/index.jsp?productId=4232163&CAWELAID=602137696 http://www.samsclub.com/sams/shop/p...CSE_Froogle&ci_src=14110944&ci_sku=sku5334071 Both are at BRU if you want to take them out to your car and then see how each fit. And likely you can get BRU to match the online price if it's different in the store.
Also in that price range would be the First Years True Fit (online, the BRU version is the Premier and is out of your budget) with a 35 pound rear facing weight limit, and the Evenflo Triumph 65, with a 40 pound rear facing limit and a tall shell. But those are also both very wide seats. So you can look at them, great seats, but you said you wanted narrower.
Wendy