I would say that's a good buy if it doesn't go up too much.
I sold scores of these on this very forum in 2012 and seeing this brought back memories !

The cancel is a London Inland section Horizontal oval with number in Diamond. It looks like 21 which would make it Woolwich or Wanstead. Dated onwards from 1844.
Good luck
Londonbus1.....loved the corner letters too !
