I can't help much with the first question. Yes, many boat builders are no longer in business.
For your second question- depends on what reasonable means.
To trailer a boat with a normal tow vehicle like a 1/2 ton pickup or large SUV and do it with no over width permits then you are limited to about 24' and 8-1/2' beam and about 5,000 lbs displacement. Lots of builders make boats in this range: Rosborough, C Dory and Ranger Tugs.
If permits are ok and you have a full 1 ton or larger pickup, then 30' is possible. A Mainship Pilot 30 weighs about 12,000 lbs loaded and has a beam of about 11'. Or a Nordic Tug 26 is a little smaller at 8,000 lbs and 9' beam. The Mainship will take a triple axle trailer to move it and a total tow weight of about 15,000 lbs. That will definitely require a 1+ ton dualy to tow it safely. The Nordic Tug probably will have a tow weight of 10,000 lbs and can be pulled with a 3/4 ton pickup.
David