i hear you, so many cool models and soo little money!

i dont own a caldera, but from what i have read they are good, but nitro and electric version. basically, they are alitte bit wider and longer than the volcano.
it costs $10 more than the volcano. i will add that from looking at the pics, the bumpers on the caldera look a bit stronger than the volcano(tho i havent broken any on my volcano yet)
i can understand your wanting to go nitro. i started in the hobby 5years ago. i made the mistake of buying a USED nitro. please dont do that! even if you decide not to go with redcat, at least do yourself the favor of getting a NEW nitro.
the volcano and tornado are great starter nitros. the SH motor is easy to tune. they are tough, and pretty quick.
for me, i like the brushless versions i have. they are just as fast as nitros, but take less work.

my honest advice: sounds like you want a beafy nitro monster truck. the caldera 3.0 or the earthquake 3.5 will fill that need best. i might be able to get you a caldera with a starter kit in you budget. then you would only need some nitro fuel to get running.