That hasn't been my experience with my TS250/1. I came across a dozen bottles of Putoline Full Synthetic 2T at a Huddersfield Autojumble some years ago - the seller was asking £1 a litre bottle, but took a tenner for the 12. I run that at around 40:1 (best guess !), as I feel that 50:1 is a value set by politicians not engineers. 40:1 burns very cleanly, giving a dry, dark brown tailpipe & little visible smoke when warm. I think I have 2 or 3 bottles left now & probably wouldn't pay £10+ a litre for full synthetic - I have a few bottles of Hein Gericke semi-syntheic I got when they closed down, and a full 5litre bottle of Millers Oils mineral 2T that came from Mark Dicker's clearance (Mark's favorite 2T oil that he used in all his two strokes), so won't need to buy any for a while anyway - particularly since the TS has only done 28 miles in the last 3 years !
Semi-synth needn't be too expensive - Smith & Allen do 5L for £18 delivered on Ebay (eBay item number: 371836178328). Or Westway Lubricants have 5L fully synthetic for £23 delivered (eBay item number:121569083858). Buy more - save more i.e Rye Oils have 25L semi-syntheic for £66 (or best offer) delivered (eBay item number:272416041052) - thats only £2.64 a litre.
When all is said & done, any modern 2T oil is going to be head & shoulders above the oils that were available when the bikes were new. I have always worked on the principle that decent oil is cheaper than an engine rebuild & choose to use oils that others may deem over specification for the application - you may take a different view.