Burn new bootloader without crystal
I've done just that on a Arduino Pro Mini of mine.

You need to change the fuses to have the chip use the Internal Oscillator, instead of a crystal. After that you just program the 8-MHz version of the bootloader. Like the one used in the Arduino Pro Mini 3.3V. 

The only problem is that you need to connect a crystal, to change the fuses to not use the crystal. Though it doesn't need to be 16Mhz. Anything between 1 and 16MHz will do.

But since you need to change both the fuses and the bootloader, there is no advantage to buy chips with the bootloader preinstalled. 

I'd just buy some bare chips without the bootloader.

PS $4.66 is on the high side for an ATMega328P-PU.