I can play the "rough estimate" game. Assuming you have purchased a SBC powered V8 gbody set aside $3k-$4k for an auto trans to hold up to anything stronger than stock, and another $1k+ in brakes to stop it all
To me " beacuse in all honesty I dont know a lot about it " means you wont be making stuff work to work with the car but rather looking to buy what already works.
SBC will be the cheapest. $2500 - $4000 will get you something that will drop in and will 100% bolt up to what you have in there now with a warrenty on the engine. Existing exhaust, wiring, cables, brackets, lines, fuel pump even your AC will hook back up. That kind of money puts you in the 290 hp - 375 hp range. Spend more money on more motor = more power = breaking stuff then the cycle starts.
BBC now you are looking exhaust and likely some fab work on the HVAC box if its an AC Car, and maybe a little clearancing to make the headers work. In and around the same price range as above with a used motor but if you cant do the work yourself and you are paying someone else by the hour to make it work for you it will add up quick. Its tight but will fit and worth the hassle everywhere but the gas pump as they tend to be a little thirsty. Going to need to upgrade the radiator as well
LS- $5 - $7k plus plus plus plus plus. Not for the faint of heart or shallow of pocketbook but as anything in life the hardest work nets the sweetest fruit !
Although I have grown to love my Monte my orig plan was to find an 86 or 87 442. ( you start with the good trans and rear that way )
Yank the 307, drop a warmed over 403, add some exhaust and be rolling again with minimal down time. Plenty of tire frying torque and a relatively quick swap. Its not a drag race winning combo but that low end torque is addictive ! Figure same or lower pricing as the SBC swap above with a good used motor.