Having built a whole bunch of cars.... I will guarantee you will be like everyone else on the planet. Which is to say -- you'll get the "well as long as I'm doing X I might as well do Y too...." The key is to control that --- and to plan for it BEFORE you get started.
$25K sounds like "plenty" -- until you get started. Then - like most builds - you'll find all manor of stuff you didn't know you needed or didn't count on.
The LS motor will eat up too much of your budget IMHO. UNLESS.... Unless you do a "take out" which is a fancy way of saying a JUNKYARD motor. Sure - you'd like to find one that has 3,000 miles on it and the car gets totaled somehow... but junkyards know what this stuff is worth too.
Frankly -- there are many more costs to this swap. Electric fuel pumps - headers - new radiator - electric fans and on and on.... it's all these little items that really add up because they're not $25 items. Just a front accessory drive for these motors can be $2500
I think first and foremost you need to be real honest to yourself - and say - how many miles am I going to drive the car - where am I going to want to drive the car - and how much time and skill do you have to build it etc.
So I'd be looking at a nice torquey small block (you can buy real decent crate motors from GM or? And all they need is a good distributor curve to wake them up) or mild big block - mechanical fuel pump - carburetor - T56 tranny - converting to a Ford 9" or built 12 Bolt (there's all kinds of "kits" out there for this) - and real decent suspension - killer wheels and tire combo... great sounding exhaust... updated headlights and taillights -- and fixing up the interior - including gauges - and steering wheel and SEATS (Camaro seats SUCK!).
I'd want a car that is reliable (we used carbs for about the last 100 years quite reliably - not to mention the reliability of the SBC).... that is fun to drive - meaning it rides and handles well - and has comfortable seats and air conditioning etc. You can get some pretty decent tires under the car with the right offset wheels and
It doesn't seem like you'd save that much dough just doing a different motor - but it's the fact that there are SO MANY options price wise for SBC's in these cars... and you don't have to run with EFI.
This motor might be too hot for a nice street cruiser -- I'm just using it for an example. This is but ONE builder - and they have several levels of performance to choose from.
Here's a pretty HOT 383 stroker motor - with 450 HP -- 460 ft lbs of torque....
http://www.smedingperformance.com/ch...orsepower.html
Couple this to a nice 5 or 6 speed and you'd have a nice cruiser.... Or if you wanted to go automatic - get a simple stage 3 700r4 with a 2800 stall torque converter and roast the tires at will.... and be under 10K -- even buying new headers and a new radiator you'd still be under. Wheels and tires - there's 5K.... now you're at 15 grand.... rear end will set you back another 5K -- with gears / axles / and coil over type kit such as SpeedTech or RideTech or BMR sell ... Then you're at 20+K -- now you have 5K left for A arms/springs/shocks/subframe connectors up front and some interior stuff.
There's nothing wrong with wanting to mini tub the car.... as long as you have some skills and the tools to complete the job. But you said you weren't interested in tracking the car particularly - so other than looks and fatter tires back there -- you're adding a lot of cost and complication for something you don't intend to use.
While 25K is a decent budget - it's going to be just barely doable IF you choose wisely.... shop for bargains when you can get them... and don't bite off more than you can chew.