Just buy the bike as is, and replace when necessary. Use any extra money you have on lights, helmet etc. I use cyclocross tyres and it sounds like that's all you would need, as 29ers would most probably be to wide for what you need.
I'm surprised your city / state charges so much for rego. Ours is only $5.

edit I just checked your link and the tyres you have are already wider than mine. I'd say it's all go go go. Mine are 32mm