Legal Implications of Aggregator App?

Hello everyone! Been reading posts for a long time but this is my first time posting.

I've started to encounter a problem lately with trying to find specific used cars (think specialty and exotic cars) but every time I search I have to look through at least 4 or 5 different websites it seems because there is no aggregator available that I can find or the search isn't that great. The closest thing I can find is autotempest.com but that seems to be missing cars or excludes large website from the aggregate.

My question is, does anyone have advice for what the legal implications may be of writing a crawler that could index these pages and pull together used car listings into one place?

Does anyone know of a contact/article they could point me to discuss further before I start putting time into developing something, just to find out that it won't be something I can release to the public?

Appreciate any and all feedback!