I'm a Canon fag so I will only recommend Canon models. If you want the absolute cheapest that will get your feet wet while still blowing away your cellphone, I'd go with a Canon Rebel 450D.https://www.ebay.com/itm/Canon-EOS-XSi-450D-12-2MP-DSLR-Digital-Camera-w-EFS-18-55mm-IS-3896-Actual-Shots/254361920764?epid=100101989&hash=item3b3926e4fc:g:UDQAAOSwwkVdgD9X
Dude has all his caps and boxes and the kit lens for a decent price. Selling for $180. Maybe offer $10 less. I own 2 of these and abuse the hell out of them. Excellent battery life too. No Video. While it's only 12MP, the quality is great.
If you want Video or something newer I would go with a Rebel 650D or 700D, used for under $300 and $400 respectively.
A decently priced 700D with Kit lenshttps://www.ebay.com/itm/Canon-EOS-Rebel-T5i-700D-EF-S-18-55MM-IS-STM-LENS-DSLR-Digital-Camera-Youtube/143338844350?hash=item215fa930be:g:As0AAOSwMkJdQe8K