I am curious where this myth about snakes feeding on mice never eating rats started. I have been keeping snakes since before most of the people on this site were born and I have never had this problem.
These days I only keep pythons including various types of jungles, Darwins, GTP's, rough scaled, SW carpets and all the smaller ones are fed mice up till I switch them to approx 70gm weaner rats.
I start all my hatchlings on fuzzy mice and they progress in feed size up till approx 40gm adult mice, 2 to a feed before they get weaner rats. There are different opinions on this but mice with developed skeletons, organs, skin and fur have much more substance than pinky or even fuzzy rats. I breed Quackenbush mice and they are much larger than common mice with young adults 35-40gm and older males up to 75gm (still feed these to my adult GTP's)
My smaller pythons, especially jungles are occasionally fed mice long after they have progressed to rats, I often have some left over when gassing and packing a batch and they go to my smaller pythons.
It is not a matter of cost for me because I breed large numbers of rats and mice but since I started selling frozen rodents on the Gold Cost I am amazed by the number of people who are terrified of feeding mice to their pythons. I sell 35-40gm mice in 10 packs for $10 yet some prefer to pay pet shop prices to get fuzzy rats?
I sell lots of hatchlings that have been fed on fuzzy/hopper mice and I do not recall ever getting a call from a new owner having a problem switching them to rats.
For the record my rodent prices with no minimum order, all vacuum packed with no water ice, discounts for large regular orders.
Fuzzy, hopper, weaner or small adult mice in packs of 15 are $10. 35- 40gm adult mice pack of 10 $10.
Weaner rats 70-100gm $3 each in packs of 4 or 6.
Small rats 110-140gm $4 each in packs of 4.
Young adult 150-190gm (Pet Barn XL are 160gm) $5 each in 2 packs.
Adult 200-240gm $6 each in single packs
Large 250-280gm $7 in single packs.
XL 290-360gm $8 in single packs.
I rarely grow them larger than 360gm because they will have a higher fat content, only a few retired male breeders.
I don't keep any rats smaller than weaner frozen because I don't use them myself but I can process some for large orders.
All rodents are fed premium food and grown in large cages designed to keep them active and lean, gassed with food grade CO2 and vacuum packed in commercial food grade bags with weight on bag.