Whilst I do not really know the Regal, the Scimitar SS1 1600 is very simple as a starter.
Fibreglass bolt on panels, most parts can be found readily, no Engine Management (It has a Carb), interesting (or ugly to some) look.
The Ford CVH engine whilst having issues re oil circulation if abused is not complicated.
Downside only two seats, upside no body rust and if you get a galvanised chassis version (usually circa 1987 onward single wiper) not that many nasties.
The tricky parts to get are the quarterlight frames,,replacement trailing arms are pricey, the electrics though not complicated seem to have a habit of losing earth so you will spend a fair amount of time getting to play with test bulbs/multimeter, but this is good training in car electrics. Fuel tanks also not cheap.
But on the positive side easy practice on brakes and suspension, the rear brakes being drums and the front discs. Also get practice replacing fuel lines (old ones perish so worth switching) and whilst cambelt removal process is simple you do have to unbolt front crossmember.
Not the car to learn to weld on (i don't) but a good car to work on with only sockets, screwdrivers, torx heads, meter, bearing pullers, and if really get the bug headwork, upgrade carbs, gas flowing can tweak performance.
If the bug takes the 1800 turbo version whilst more complicated can be tweaked to give interesting performance (though insurers may not be as keen as some have been modded well beyond road use)
Price wise re the 1600 non runners at £400-600, runners say £1000-£1500 and really sorted say £2,500-£4,000
Whilst cheap there were not many made (about 1500) so eventually if you wait a lifetime they may go up in value further.
If you do not mind rust/welding an old VW Beetle or Morris Minor is mechanically really simple.
If I was to go for any still cheap(ish) classic it would be a volvo 1800, but their price is getting a bit high, the Trimph Spitfire is another low cost entry.
If i had a choice of classic (money no object) an early mark 1 Escort would be my choice, but that is due to sentiment (second car, first was a mark II cortina), but a cheapish one (£5,000) will need welding skills , a rust free will be expensive.
Other plus is classic car insurance can be very cheap, even if a younger driver, I think they must base it on the fact the cars are often not on the road.
Vested interest-I have a currently off the road Scimitar SS1.