What models are you comparing? There's some big construction differences between them in general such as floors with framing on 16"oc, enclosed underbelly, different chassis/running gear. Our HG is a step above both and loaded and I negotiated a price just a little north of your $20K mark...
Not sure where you are getting prices, but RVWholesalers typically sells the MiniLites for the teens, UltraLites for the teens to low 20's and the Signature UltraLites for upper 20's to low 30's. I think since you are stating 28' maybe you are confusing some of the model lines??? Sounds like maybe you are talking about the UltraLite versus Signature Ultra Lite. Like geo stated, there are some differences in construction, as well as standard features and included amenities.
Hi woozy! DW and I purchased a 2015 232IS with every available option except rear ladder. It's a "couples camper" that FR has now discontinued. We did not buy local for two reasons 1) our local dealers carrying FR either a) are terrible for a variety of reasons or b) didn't carry lines we were interested in, and 2) we needed to buy for dealer inventory because of the circumstances we were in late last season. Ultimately, negotiations narrowed down to two dealers with identically equipped units - one 5.5 hrs from us and the other 8 hrs away. Either were willing to sell to us a few hundred over cost, which amounted to 35% off MSRP. We chose the unit 5.5 hrs away because DW preferred the interior fabrics.
I'm a repeat FR owner, and our last camper with a Shamrock 21SS where the construction is essentially the same as the minis. The HG is much, much more in every aspect.