Other than making curtains to fit, the cheapest I've done (when replacing worn out factory day-night shades) is to get off the shelf mini venetian blinds from Home D or Lowes, They'll cut them to specified width at no charge, and its not difficult to shorten them to proper length. I put the mount clips in the same location as the original shade mount clips. The decorative valences, original to the trailer, may take some inventivness to remount, as the mini blinds hang further away from the wall than the original shadfes (I left mine off).
I used aluminum mini blinds (v. the plastic type), because they won't let light through when closed. We prefer to not give sillouette shows to our neighboring campers!
1967 17' Hi-Lo Bon Voyage (1967-1969)
1969 19' Hi-Lo Bon Voyage (1969-2011)
2004 27' Hi-Lo TowLite (2010-present)
2015 Chevy Tahoe LTZ