Depending on how many guests you are having, things can defitenly add up for the OOT bags. If you are crafty and have the time, you can totally do a lot of DIY projects to help cut down on some of those expenses.
I am doing them, but only b/c I am having less than 20 guests and I caught a lot of bargains.
My advice would be to make a list of everything you want or would include in the bag, do a price estimate and see how it goes. Like the other posts said, stick to a budget of per bag. Another expense you have to take in consideration is how you're getting the bags to your destination. With these weight allowances chaning with the airlines, you may want to be leary of that fact as well.
In all honesty, guests can live with or without the bags, I just thought it was a nice, inexpensive, touch to show them my gratitude for traveling soo far for our special occassion :~)