I can't speak for 'down South' but up here mostly folks want purebred tups yes (you cross the ewes but not the tups, if you do both there is too much variation in the outcomes), but particular crossbreeds are sought after, eg, Dutch Texel cross Texel, Beltex cross Texel, Beltex cross Charollais. And it is known though not openly discussed that certain breeds get an occasional undocumented sprinkle of something else (many Hexhamshire Blackies contain a bit of Swale, many Swales a bit of Blackie, most good crossing Blue-faced Leicesters - ie, those used to sire North Country Mules not those used to breed pure Blue-faced Leicesters - have a bit of Teesdale or similar.)
In terms of selling tups for > £100, the most important thing is your name. If you have a name for breeding good tups, buyers will have the confidence to try one a bit different. If you are unknown you may not get £100 for a really good purebred registered tup, because it's not just about looks it's also about breeding and how it's been reared. If there is a show-and-sale at which you can get a ribbon for him then you may get into the better prices, but it's still not guaranteed. Similarly if you keep him on and work him as a tup lamb (you could loan him out if you don't have spare unrelated ewes yourself) and can get some ribbons for his offspring then sell him as a shearling tup with that history.
Mind, I am talking commercial farmers as buyers not smallholders.