well, autocad and max is roughly 9k USD...
you can get maya complete for 2k, if you add a copy of lightscape for 800 you can render impressive interieur radiosity lightsimulations for about 1/3 of the price.

If architectural visualizations is (and will be) really all you want to do, you won't need mayas animating powers and I might even suggest to look in the LightWave/Lightscape combination (about 2300 USD total); LightWave's renderer is extremely good at exterieur radiosity and Lightscape can handle the interieurs...

sticking with the discreet line of products will of course make the process a little (if not very much) smoother, but you have to decide if this is worth the extra ca$h.

after all you have to see what works best for you, which package/combination you feel the most comfortable with...