The 2013 Dell Venue 11 Pro is remarkably good a contender. It's been $300 for half a decade, has 8-9 hours battery life with the keyboard, isn't super light nor thin but is pretty good & very compact, has a decent front shooter & so so back shooter. Has a 4G option.
I have moved on to a great 2-in-1 from 2017 that is quite similar, newer specs, much lighter at 7.4mm and 1.6lbs, OLED screen... this isn't geek pride. This is a fantastic brilliant light machine that until very recently would knock the socks off any iPad or Android Tablet, and has been available New Old Stock for under $400 for years now. It's far more machine than the flagship tablets until very recently.
The low end iPad is definitely an enviable marvel but it's also far less of an advance than I think we really understand. Part of why it looks so good though is because so many machines are poorly built, are compromised heavily. The whole 2-in-1 thing has gotten segmented into expensive fancy Surface competitors & ultra-low-end machines (which honestly with slightly better builds and much much better screens would be stunning devices), with unreasonable uncompromising top or bottom of market positioning. It's been sad. But some places out there are some really great 2-in-1 pc competitors, that have long put to shame Android & iPad offerings (until Apples very recent speedy but oh-so-limited oh-so-walled-garden oh-so-controlled shorter-lifed iPads).
There's absolutely a lot of people who just swear by Lenovo T420's forever & seemingly always will. I'm not at all of that ilk.