Yes and no..It pretty much comes down like it or not, to what you want to pull out of your wallet and put into the car...Because if you already have a ka that needs a rebuild, your $2-3,000 up because you already have the motor..Another thing, if you buy a sr20 for a swap, I would HIGHLY suggest getting the whole front clip, that way all the parts are there for the swap, and there are a minimum amount of parts that would be missing...Also, once you get the sr20, you have to take into account labor, unless you plan on doing it yourself, which I definitly wouldnt suggest unless you know what your doing. Most shops charge around 75-125 an hour for labor, and on average, a motor swap takes anywhere from 5-15 hours..so thats another couple grand.. and even after you get the sr, and then finally have the swap in the car, your still stuck with a stock sr20..so lets do the math for each, for a ka rebuild with turbo, and a stock sr20 swap. Rebuild for ka, you have all the parts, depending on how in-depth you want to go with the rebuild, if you want all forged internals, or oem.. your looking anywhere from 750-2,000. and thats 750 oem, and around 2,000 forged.
then take into labor. About 6-10 hours for rebuild. thats anywhere from 750-2,000 in labor..then the turbo if you decide to do that then. say around 3k for a good kit..then clutch and all other necessary items needed for turbo motor, ie. fuel pump, injectors, f/i controller, boost controller, timer, etc.. most of that is not included in the turbo kits. so for a complete kit, your looking at about 5-6,000. then another 5-10 hours for labor, and then tuning. So all in all. for a ka rebuild and turbo, your looking anwywhere from 6,000-10,000..and I know thats a broad range, but there are alot of factors that determine your outcome..for example, brands, prices on different products, what shop you use, if you do anything yourself, etc..but its a general idea.. Now for just the stock sr20 swap..your going to need to find a good sr20, if you do the front clip, your looking anywhere from 2,000-6,000 without shipping.. Now for labor, a complete swap is from 1,500-5,000.. and thats just for the stock sr.. so ka rebuild with turbo is about 6-10k(300-500hp), and a stock sr20 swap is about 8k-15k(180-210hp).. then if you want to build your sr20, your looking at another couple grand.. so like I said it all depends on how much you want to get into it, and how much you want to empty your pockets.

ok but any 240sx i get is going to need a rebuild n that as much as buying a sr20 with 40k on it.

also look at this post, alot of good, useful info in it as well
http://www.240sxforums.com/forums/beginner-s-forum/55363-all-engine-swap-information.html

The sr20 has more potential i guess.. but thats if you want to spend the time and money on it...im talking 10-20,000+.. The ka24 is a great motor, and has alot of potential as well...and generally it is easier to find replacement parts for the ka...just keep that in mind..another reason people chose the sr is because it is lighter than the ka..but if your just buying it to add minor bolt-ons, exhuast, cai, possibly turbo, the ka is fine. I saw you looked at mine, I have the ka in mine, and Im now pushing over 500hp through it, and it is still my daily driver that I carry my 1yr old son around in. and I trust it to do just that. Once you start spending BIG money, and getting into it alot more, then start looking at the sr20 or the rb20, 25 or even the rb26...I would love to do that, but then it goes back to the whole budget thing.. Im 22yrs old, with a 1yr old son. I work my ass off to support my wife, my son and myself..so what little money I do have left over goes proudly into my ka.. But just starting out, especially on a budget, the ka is just fine, and you will be very happy with it. You wont be able to tell the difference, and it is still a GREAT motor. Hope I helped a little, and let me know if you have any other questions