I just want to know what the minimum temperature outside should be when I go out to buy a new hamster

Why would the outside temp matter?

Are you concerned with transporting the hamster home? Is that what you mean by your question?

Hamsters are pretty hardy. If it's very cold where you live right now, than have someone start the car and let it warm up before you take hammy out of the pet store. Get the person to pull up to the door so you're only outside for a few seconds.

Same when you arrive at your home.

I live in Indiana and it's supposed to be in the 30s this weekend.

That's not too bad. I've brought a hamster home when it was -22F outside.

Like I said, let the car warm up, make sure it's nice and toastie, and get someone to come with you so that they can pull up to the front of the pet store when you come out.

A few seconds in the cold won't hurt your hammy. :)

because it isn't good to get animals when it's too cold but I got one today since it was decent weather! =)

I actually ended up getting one today since it was in the 50s! =) and thanks for you help!