A 2017 iMac should be able to update to Ventura just fine.
There are a number of drives out there that will work with it.
What is your specific concept of "cheap"? You can get a good quality 500GB NVMe for around $100 USD from reputable sources such as OWC with good warranty and support, or a cheaper no-name alternative which may or may not work or cause issues from places like Amazon for around $50 USD.
click here ➜ https://eshop.macsales.com/shop/ssd/owc/imac-27-inch/2013-2019
or here ➜ Ranxiana NVMe for Mac, 512GB - Amazon.com
Also note, that installing the drive internally, will require complete disassembly of the iMac and removal of the screen and re-attachment, which is not a simple job to attempt since it will require new adhesive strips for the screen, and a very careful removal of the glass which can easily break.