Shari - I've found if I don't have my scale, I LIE to myself about whether I'm on plan or not and gain! True story! I'll believe I was TOTALLY on plan, gain 4 lbs by the time I return to my scale, and then think back on all the junk I ate and realize what I've done. Something about having to get on the scale the next day keeps me honest.
Do what you have to do. At least you can get a cheap one...you can still keep an eye on whether it is moving up/down or staying even, even if the weight is off.