I think you can ignore the 26R in your case. the R stands for racing. It is a Racing car at Racing car prices.
Fully restored Road Elans are advertised (when available) by some of the professional restorers at ?29,000 -> ?40,000 but they are usually immaculate and as original as possible; better than when they originally sold from Lotus. Whether they actually manage to SELL at these prices is not really known and if so they probably just go into a velvet garage in the hope that they will increase even more in value.
In My Opinion:
Good driving condition Elans are probably in the price range ?12,000 -> ?20,000 depending on condition, with smart well maintained ones at the top and well used ones at the bottom.
Condition will usually override which model it is but the S1 and S2 will have a price hike due to their rarity and the S4 with a price hike because it is the later model and may have more convenient modernish bits like Alternator instead of dynamo, yet still be original. Sprints are basically a hotted up S4 and have an even higher price, they are also relatively rare. So of the running cars the S3s are likely to be slightly cheaper. Coup? models are usually less expensive than open top (roadsters) because of the thrill of driving with the wind seems to attract some people. They appear to forget that it often rains in the UK.
Renovation jobs price from about ?6000 to ?12000, with field-finds at the bottom (exposed to the elements for 20-40 years) to Barn-finds ( chicken & rat dung but basically dry) to cars which have been off-road for 5-10 years for repair/renovation through to runners in rather poor condition.
There will be a price hike for early S1,S2, Sprint for rarity and then S4 priced higher than S3, but the main pricing factor will be completeness and lack of deterioration of the main body and doors and seat frames. You will normally expect to have to replace the 'chassis' (officially a sub-frame for the DVLA) of any 'Find'. Cars with 4-inlet port heads (Weber/Dellorto) heads will generally be priced higher than those with the two-port (Stromberg) heads; but of course most of the cars in the USA are Stromberg ones.
Strombergs get more MPG but a bit less power than Weber/Dellorto cars.
Unscrupulous owners in the past may have tried to disguise an Elan as one of the slightly more valuable versions. painting S4s in Sprint colours and attaching Sprint badges and stripes is common; enthusiastic owners may have done the same, merely to feel good with no unscrupulous intent. Certain members on this forum can determine if a car is a genuine Sprint from its VIN (vehicle identification number) which is on the plate in the engine compartment on the Exhaust side.
Elan Plus 2, S130 etc are the models with two child-sized seats in the back. Basically the same car, but bigger, with many components the same as the Elan, but somehow considered less desirable and generally priced ?1000 to ?2000 below an equivalent Elan two-seater. I don't know much more about Plus 2s myself, so I will leave any further comment on them to the Plus 2 owners.