UPDATE: Reviews section refreshed, redesigned, searchable: Go take a look
Deore is only in 10sp isn't it? SLX is cheapest 11sp I think. But apparently Deore is available in 11-46 just the same? It's for my daughter's bike, she probably won't notice big gaps in the range.
Also depends if you have a crank or not
https://www.chainreactioncycles.com/groupsets?f=2258,4294963609,4294125265&sort=pricelow
Looks like I can get 10sp Deore for about £80-90 from CRC. We have a crank, it's 155mm so probably not worth changing and cost needs to be minimised.
Slx 11 speed on ebay for £135
I have an old 10spd deore mech that works nicely with the slx shifter,<span style="font-size: 12.8px;">I bet the new deore mech will work with the 11spd shifter.</span><span style="font-size: 12.8px;"> </span>
