Actually you can still buy a
new iPhone 7 from Apple, or a
refurbished one from Apple, and I assume other retailers. Apple has its annual new iPhone event on Tuesday, so that might change what is available going forward. Pretty expensive getting one through Apple though. You might try getting a monthly payment plan through your cellular provider if you have a data plan.
If you get one through a site like eBay beware of warn out batteries. Be sure to ask as many questions from the seller as you can think of. Request that the seller show you the battery condition screen from the iPhone 7. The iPhone 7 Plus had a much better battery, BTW. I went from an iPhone 6 Plus to a 7 and regretted that move as the 7 needed charging every day. The 6 Plus lasted much longer before needing to be charged. But the Plus models are bigger and bulkier to carry, if that makes a difference to you. I was happy to get my X
R and have great battery life again.
You might check places like Walmart and Best Buy for deals, especially after Tuesday. Once the latest greatest gets released, or at least announced, the prices on the 7 might come down a bit. If Apple discontinues it, then the prices should drop as retailers try to get rid of new and refurbished stock.
Good luck!