Does the 'normal' Developer package include access to Templates, T4 Page Builder and Extensions?
Can you clarify if you were referring to the templates & extensions at only JoomlArt? If so then yes, Developer membership package has access to everything at Joomlart (templates, extensions, T4 page builder).
I understand that, but I don't want to be locked into something that may go up hugely in price.
Actually if you purchase Ultimate Developer bundle when it's available at $299 then you can renew it at this price range (plus 20%OFF renewal discount).
For comparison between Developer membership package and Ultimate Developer bundle, please check our Pricing page.