Unfortunately you are pretty much stuck with the cost unless you can do the work yourself. It's very rare that any glass place will reassemble the unit even though it isn't that hard. Most places will just measure and order a new, already assembled double pane unit to install. I've rebuilt about twenty individual dual pane windows, and while new spacers and sealer aren't expensive, it's quite labor intensive. At a shop rate of $90 an hour it would get expensive to have it done.
You have to remove the window frame from the coach, disassemble the frame to remove the glass, cut the spacer apart - not needed in your case - and remove the sealer and spacer stuck to the glass. Then thoroughly clean the glass, apply new spacer material, assemble the two panes and backfill the edges with sealer. After drying 24 hours, install the glass, assemble the frame and reinstall the frame in the coach. It can be done if you are handy. You can buy a rebuild kit from here:
https://www.daverootrvglassrepair.com/
Or you can do what I did and order the individual materials from Amazon. Read the info on Dave Root's site to determine which is the proper spacer size. The Spacer and sealer are made by cr Laurence. Search for cr Laurence super spacer and you'll find plenty. Comes in 66 foot vacuum packed rolls. Sealant is CRL Super Spacer Sealant. While is isn't required, the sealer applicator block is handy: C.R. LAURENCE SGT316 CRL Polyethylene Sealant Guide.