I will freely admit that few people are cheaper than me when it comes to sleepwear. I laugh at the $29 lounge pants and $36 slips and instead wear old tank tops from college and knit shorts that I got for $4.99 at Target. However, I think it is important to have at least one set of presentable pajamas for the times when you're staying over at someone's house during holidays or (eek!) staying with a boyfriend's parents for the weekend. You need to keep your assets covered, which is easier said than done in a lot of the options in stores.
Here are some options that are fairly reasonable in price and will not cause embarrassment when your boyfriend's dad sees you brushing your teeth in the morning.
Victorias Secret Boxer Pajama - $25
Victoria's Secret Racerback Pajamas - $29
Target Cami/Crop Pajama Set - $19.99
Gap Body Stretch Jersey Robe - $39.50
Old Navy Racerback Chemise - $15
Notice I put these together - that little gown is pretty skimpy, but with the robe it would be decent