Will they combine these?
 

I'm currently holding a Budget reservation in Las Vegas for 2 days at $42 all-in, with a 3rd day for $32 all-in. Currently, to book 3 consecutive days is over $150, so I'm more than willing to trek back to the CRC to re-rent the car. But of course it would be ideal if I didn't have to.

What do you think my success rate would be at the counter to have these 2 res combined at the lower rates ($74 total)?

What do you think my success rate would be if I CALLED before the expiration of day 2 and asked to keep the car for another day (not mentioning my other reservation?). Do you think it would be for a reasonable $20-$30 upcharge or a ridiculous $110 or so more?

All were booked through Costco.

Any personal experiences?

And yes we need a car in Vegas since we're doing lots of things where a car would be helpful.

You can call the day of and check about extending it. It might re-price, though. My guess is that you'll have to trek back to the rental car center.

With Avis, I've had this many times and only once have I been able to call and them check-in the car and check it out again. It's against the policy (what if you damaged the car and had insurance on the 2nd rental, etc), but it was a local station and I knew them well.

Budget does have several city offices owned by the same franchisee as the airport. They may be able to handle the transaction for you.