I forget whether you have a tow vehicle already or not, but when you mentioned "Casita" that got my attention.
I have been looking at Casita travel trailers off-and-on for a few years. At least in my area (northern California), a Casita in reasonably good shape will set you back around $12,000 - $15,000, a new one from the Texas factory around $20,000 +/-.
I have actually looked at several over time (still looking, for that matter), as they come up for sale in my area. Pricing has been from from $15,000 for a really nice one in excellent shape, down to $6,000 for 25 year old Casita that was basically beat to death (no AC, no fan, no tanks, wall carpeting was nicotine-stained blue hi-low) that also had large wall cut-outs in the fiberglass in the interior trailer walls that the current owner had made for God-knows-what reason.
Keep in mind that the Casita is a form of monocoque construction - the fiberglass shell is also the trailer's "structural skin", thus the loads are at least partially distributed and supported by the fiberglass (bending and twisting loads created by the mere fact of driving down the road). Similar to an egg shell (a Casita is also often referred to as an "egg shell trailer"). Take away the some of the supporting structure of
any trailer (for example, cutting out sections of the fiberglass wall on the interior of a Casita!) - and you are going to have problems (probably major problems) later on.
I was thinking that this egg was likely crack at some point. Scrambled egg, as it were.
At 55 mph. No thanks.
Add to the cost of a Casita the additional $15,000 - $20,000 for a decent used tow vehicle (and lucky to find one in this price range) - and you are already well up into the used Class C range so far as pricing goes.
However, The Great Truth often stated on this forum is that these kinds of decisions are specific to the individual making them. What works for someone else, might (or might not) work for you.
Good luck in your search.
Anne