Unless your space is really large, and/or you like to listen really loud, you probably don't need an external amp.
In any case you can start without one, and if you really feel the need, you can spend the money on the amp later.
Quickly checking prices (they're higher with less stock available), the big price jump happens when you go from 5.1.2 (7 channel, currently $400-$600) to 5.2.4 (9 channel, currently $1300 and up).
Many of the 9 channel AVRs process 11 channels, and "just" need an external stereo amplifier ($125 or less) to power the extra channels.
Closeout, Open-Box and Refurbished items can bring the price down to that $1K mark but that's very hard to find now.
Refurbished of course offering lower warranty (typically can be supplemented or upgraded).
Used items on ebay are sometimes available with a 3rd party warranty.
If budget is a high concern, you may want to start with a used/2nd-hand 5.1.2 AVR now, then replace it when supply improves later. It may actually cost less in total than buying a full-price AVR now.
Thank you for the info. I am wondering if I need an external amp in addition to receiver for better performance or it doesn't really matter?
Looks like there is huge jump in price if I chose to do 7.2.4 vs 5.2.4. I guess I need to be realistic if I don't want to spend more than ~$1200 on receiver. Denon X3700-H is one option I'm looking at it.