The cost will totally depend on how much time you want to spend finding the right deals on used parts, if you are in no rush a swap can be done fairly cheap if you're willing to wait for deals to pop up. when i did my swap i bought everything new except for the motor and transmission but i ended up rebuilding both. My swap was way more than $3500 but i have an ls2 with a strocker cam intake ported heads, fuel cell, aluminium radiator, custom tune, rebuilt t56, bought my mounts from jci, sanderson headers. My setup is made to handle more power than i have now so i have room to grow if ever i want to.
questions you need to ask yourself:
Do you want an aluminium block or iron block?
Do you want a 6 speed, 5 speed or automatic?
Do you want to upgrade you cooling system?
Are you going to tune the engine yourself or get a tuner?
is your fueling system good enough?
are you going to build your own mounts or get a kit?
are you going to rewire your harness yourself or get it done?
new driveshaft or shortened one?
drive by wire or drive by cable?
are you going to sell your old setup?
you have a running setup right now, if you wanna go ls i would suggest you get all the parts you need before taking your car apart over the course of a year i'm sure you could find good deals on any of those items. If you peace your swap together over the course of a year you might free more funds for the swap too. it's easier on the pocket book.