I'm also on a very tight budget as I think most people are right now, so today I thought I'd share some of my favorite slips with you. Vintage slips tend to be under $20, and if you choose cotton fabrics, it won't look like you've forgotten to get dressed.
Vintage white Cotton Slip Dress $12 www.zibbet.com/BlytheHopesVintage
Or choose one with lots of pretty details like this:
Vintage 70s baby blue Slip $9 by yeahimgroovy.etsy.com
Longer half slips can also be belted and make fab dresses as demonstrated here by thelasthurrah
Vintage half slip dress $10
I'm also a huge fan of bed jackets in the summer - they make for super cute cardies on summer nights. Though generally a bit more expensive (especially the 30s and 40s ones) they'll go with lots of different outfits - so it's worth the investment.
Vintage 1930s Bed Jacket $78 HauteCountryVintage.etsy.com
Vintage 70s Bed Jacket $10 BlytheHopesVintage.etsy.com
Vintage Lace Bed Jacket $15 by KlassyKlassics.etsy.com