Spend more money on the amp or the pre-amp?

Yes, i agree with the suggestion to find a vintage Japanese integrated amp/preamp//tuner.   The higher power Pioneers my favorite.

But for $800 make sure that 40+ year old vintage piece has been truly refurbished not just cleaned 

Nakamichi CA5 < $300 and PA5 < $500, can't think of any integrated < $800 can beat that combo

It depends. Do you you need a phono stage, tape loops, HT pass through, how many line level inputs.? Perhaps more importantly, how much power into what kind of impedance load do your speakers need in your room? Depending on the the answers to the above, you might find some power amps that are suitable for use with some fairly inexpensive passive pres.

Mostly great suggestions, but I would advise caution shopping for used or vintage equipment unless you are prepared to work on it yourself or pay a technician $85.00 an hour.  At the OP's price point, paying for repairs or upgrades is probably not an option.
Seems strange to say this on Audiogon's forum.  This is actually a great place to buy used equipment, as most sellers are audiophiles themselves and know the value and condition of what they are selling.  You will usually find good, fair deals.  When shopping on the open market, however, caveat emptor.