Do what I did, ask for the cheapest smartphone they had in stock. It was a Motorola but it was only $150 compared to the $900+ iphone they wanted to sell me. Could have gone cheaper with a flip phone but I need Google maps. Then you can use your money for other things.
If you must use an iphone then maybe ask for a used one or something. No need to break the bank on a phone you'll probably have to replace in 1-2 years.
Most Iphones either slow down to a point of annoyance or break within 2-3 years. Though I'm the same as you in the fact that I'll keep a phone till it breaks. First phone was a flip phone and I carried it for nearly 5 years.