If you go that route , it can be an adventure as you have no idea where you will be going & when, until AFTER you commit. Personally, if I have time and am flexible, I often go for the unknown. Your dad may not be up for that. Also, check the fine print - I'm not sure if Priceline adds in taxes, service charges etc. I know they DO NOT on hotels, but not sure on air. I've never been able to book any decent air there.
Given that you can check their normal routings & pricing, you may be able to pre-determine what your discounted routing might be.
Depending upon your options out of SD, you might also give HOTWIRE a try. Do it anyway, just for comparing to Priceline. HOTWIRE does not add in any additional costs - what you see is what you get.
Downside to both of these, if it matters, is that flights are not eligible for frequent flyer mileage accrual.