You can do the change by using the
org-mode-hook, like this
(add-hook 'org-mode-hook (lambda () (set-frame-font "Inconsolata" t)))
Which will change the font whenever you enter org mode. The downside is that it doesn't change the font back after you leave org mode.
Edit: as pointed out by Ryan, you can follow the advice on this wiki page to do it per buffer. I haven't tested extensively, but this seems to work
(add-hook 'org-mode-hook (lambda ()
(setq buffer-face-mode-face '(:family "Inconsolata"))
It might have issues if you want to use
buffer-face-mode in other buffers, but if you only use it for this then it should work.