I don't really thing a divider made out of cardboard or foam board would work. It would absorb humidity out of the air and would just get nasty once the snake used the bathroom.

I think putting the snake in a 15qt tub for the first year is a good idea. It might look small to you but the snake really doesn't mind. They like tight enclosed spaces. They aren't really the kind of snakes to just lay around outside their hides.

Sounds to me like you aren't in the US so I can't really tell you what local stores to go to to get everything. D:

Basically what you need for a tub is 10g reptile heat pad, reptile thermostat, water bowl, two tight fitting hides, paper towel substrate.

Shouldn't cost you more than $60 USD total. You can even make your own hides with upside down plastic bowls.

Once the snake is about a year old you could move it to the 30g.

BTW, is it really 30* in your house? that is like...so hot..