A used car dealer would not and cannot give you a low rate financing. That's where most of their profits come from, people who make bad money decisions.
If you need to finance, get a personal loan from a bank would get you a much better interest rate.
For the Santa Fe, exactly what is the work that needs to be done and who is suggesting it?
In general, most CEL are for emissions control and really don't affect the reliability of the car. So you could drive it, just being annoyed by the light.
https://www.yourmechanic.com/article...ngine-light-on