Ok, now you have a few things to work on...
Maybe if you had money set aside for a car, and then 'blew' it on the snake, I could see why they feel that way, especially if they don't see the value in the snakes, or the money that can sometimes be made while enjoying a hobby.
I think if you show that you responsibly set aside and save some money in order to buy your own snakes, there should not be a problem with that.
I would agree - rat production is an intense job, to say the least..
You may think it does not smell, or get used to it, but someone who has nothing to do with them and steps anywhere near them will almost be knocked down by the smell !
Another thing is that some people think their food, or the rats themselves, will attract other rodents... the bad, house pest kind.
Maybe they think it will attract insects and/or other animals.
Perhaps you were 'wasting their space' with your rat group.
Either way, as mentioned, the frozen rats are they way to go.
Some advice with the Frozen rats though...
* If you will have more than a few snakes, you will want to buy your own small freezer, to avoid using their freezer, which they will most likely not like.
The rats take up a lot of space and are known to 'freak out' the ladies.. dead or alive.. lol
* Another thing is to develop a method of thawing the rats that will not upset them.
Not in the house (smell), definitely not in the microwave or oven!!!
I would suggest laying them out on a rack outside, in a garage or shed even.
I'm sure you can find some temporary enclosure and supplies for a good price so you can safely and adequately care for your boa without having to go out and spend a few hundred dollars all at once to get all top of the line equiptment.
That can come later, with time.
Going about this in a methodical way, slowly and well informed (reading and researching ways to do this) will help show you are serious and responsible.
Acting in an impulsive manner would make them not think it's such a good idea.
Overall, I think keeping the boa will help you become more responsible overall. Producing boas is a wonderful, beautiful thing... seeing life appear in front of you, seemingly out of nowhere... even they couldn't resist being intriqued and amazed if they were to see that. If you do manage to produce a litter and sell some off, I think that may change their minds about the money part.
Just my $.02
Hope it helps!
Later - Joe

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Thanks and take care - Joe Rollo
'Tis not the stongest of the species that will eventually survive, nor the most intelligent, but the one most responsive to change' Charles Darwin