Lidl Parkside (Scheppach rebadge) Couldn't find it
Titan -
Screwfix brand? Couldn't see any Titan Plunge or Circular Saws though, think they're discontinued.
The Lidl Parkside comes on sale only once or twice a year, so you have to look out for it. It is most definitely NOT a Scheppach clone and AFAIK uses a subtly different track
The Titan saw has been variously rebranded Erbauer and Macalister. B&Q have sold some of these in the past (the three brands are house brands of the Kingfisher group who own SFX and B&Q AFAIK). The newer Erbauer design uses a "185mm" saw blade - and BTW 184mm (7-1/4in) is a standard B&D and deWalt size and is readily available, so getting replacement blades won't be an issue. I'd suggest that 185mm is probably a mis-conversion from inches by someone who isn't aware of industry standard saw blade diameters
In the DIY field other notable models I can think of that you didn't include are the Einhell TE-PS (and not TE-CS) from Toolstation (or at least it was at Christmas), etc as well as the well known Triton TTS1400 which utilises a Festool/Makita-profile rail
Your list of trade rated saws is also very incomplete. The readily available plunging track saw models in the UK are:
Festool profile rail
Festool TS55R (160mm)
Festool TS75R (210mm)
Festool TSC55R (160mm, cordless, 1 or 2 batteries @ 18 volt)
Makita SP6000 (165mm)
Makita DSP600/DSP601 (165mm, cordless, 2 batteries @ 18 volt)
Metabo KT18 LXT 66 BL (165mm, 1 battery @ 18 or 36 volt)
Virutex SRI 174T (160mm)
Mafell profile rail
Mafell MT55cc (165mm)
Mafell MT55 18MBL (165mm, cordless, 2 batteries @ 18 volt)
Bosch GKT55 GCE (165mm)
Bosch GKT18V-52 GCE (165mm, cordless, 2 batteries & 18 volt)
Metabo and Mafell share the CAS battery platform
deWalt profile rail
deWalt DWS520KT (165mm)
deWalt DCS520T (165mm, cordless, 1 batteries @ 54 volt Flexvolt) - there is also an 18 volt version of this saw available
But as you say, all high budget. Information supplied for the sake if correctness and completeness
The significance of the rail profile becomes apparent when you need to do multiple full length rips of 8 x 4 sheets. If you don't have a 3 metre rail (and only Festool and Makita make them) you need to join together multiple track or rail sections. The Mafell rail system is better at this, but very expensive, so most manufacturers opt for a copy of either the older (single joining bar) or newer (two joining bar) Festool-style tracksit Single bar systems have problems keeping their straightness moved around much, and whilst they are better, even the two bar rails can be knocked out of straightness if roughly treated.That makes using some of these DIY systems which only offer 700mm rails a bit of an issue. You can straighten a pair of joined 1400mm Festool or Makita rails by holding them upright and delivering a sharp tap on offcut of carpet on the floor with the bottom of the joined rails. I'm not certain that would work as well with 4 x 700mm rail sections joined together. So maybe having a system where the rails come in 1400 or 1500mm lengths is worthwhile after all
As said earlier, though, if you are on a budget and don't need the plunge facility you can always go with a conventional circular saw and just make your own guide