It probably wouldn't be a bad idea to touch base with your wedding party and see how many intend to stay overnight. Then you can find a local hotel and call to block off some rooms. This will assure that your guests will have rooms and most hotels give a discount for groups. However, it is not your responsibility to pay for their hotel rooms. I've gotten hotel rooms to attend several weddings and never had a bride and groom pay for them.

My guess is that most people wouldn't plan to stay overnight if they only live at most 90 minutes away. Heck, that's an ordinary workday commute in some cities! But maybe some of your guests will want to make a weekend of it, especially if there will be other events (like a rehearsal dinner, brunch, etc.).

Regarding paying -- relax! Jaims has it exactly right. The hosts arrange a block of rooms at a local hotel, both so that all the guests will be at the same place, and also because you can usually get a group discount. Give the info to the out of towners and let them make their own reservations. But the hosts definitely don't have to pick up the tab for the hotel rooms. Like Jaims, I have been to many out of town weddings, and none of the hosts (including a super-wealthy family) has paid for the guests' hotel rooms.

My understanding is that the traditional etiquette does involve helping with the accomodations of the wedding party (i.e., bridesmaids and groomsmen) but not other guests. This need not involve hotel accomodations. It often as simple as (oh, bridesmaid A, can you find a spare bed in your home for bridesmaid B?).

Personally, I think an hour and a half is rather a lot if they are going to make the round trip again the next day. And especially if they are going to make the round trip at night after the rehearsal dinner (serving drinks?) and again the next morning.

All that said... I don't think it's often done anymore (i.e., helping with accomodations).

My understanding is that the traditional etiquette does NOT involve helping with the accommodations, not even of the wedding party, either! Maybe Mary has known some nice and generous folks who have done it (and I agree, if it's a matter of calling in a favor, the bride & groom should do it).

My vote: call them (they're supposed to be close friends or family, right?) and ask if they're planning to drive home, or stay overnight. Then say, "Do you want us to find a place you all can stay? I'm sure I can find something everyone can afford--Hotel XYZ is close to the rehearsal-dinner spot, and their rates are very reasonable, so I hope you'll be able to afford them."

Then you'll know, and you'll have hinted that YOU are not able to pay for that bill.