Let me get this straight. You recommend buying the center and bookshelf pair, then get rid of them and buy something better. Is that right?
Yep, I'd consider the AVR, sub, and surrounds to be good for awhile.
I see what you are getting at, it is a bit ironic/perverse!
Even though the center and bookshelves are the impetus for putting together this system, they also happen to be the weakest links in the system; the AVR, Sub, and (same bookshelf as) surrounds are more suitable to their role for a longer period.
The reality is you simply would not want to pay less for an AVR (at least among offerings I know of). Something like an open-box Pyle may be less, but I cannot recommend it because I worry about reliability. Down grading the sub just doesn't save much - the SUB-800 is $100 and the SUB-1000 is $120 (just like the 12" Monoprice), and relative to the overall budget the sub-800 costs too much to be a deliberate short term compromise.
The beauty of the front 3 for $52 is they do not steal much of the budget from the rest of the system, and you won't take much of a hit when you replace/upgrade them.
Let's just call them sacrificial speakers!