How much will it cost me to buy second hand m3 engine for a e36?

Answer 1

It depends if you're based in the US or UK. While many askers and answerers are mainly based in the US, you seem to be based in the UK. Prices of course do vary greatly between UK ad US (probably a lot cheaper in the US).

Also, the UK M3 engine is very different (and much better) than the US M3 engine for the E36. The euro-spec M3 (S50-B32) engine produces 321bhp while the US version (which used a completely different engine) only produced 240bhp.

Here're a few UK places to check:
http://www.tmmuk.com/citybmw/listings/4.html
http://www.rawspares.co.uk/bmw_car_spare_parts.php
http://195.82.120.34/cleaves/index.lasso
http://www.diymotorist.co.uk/
http://www.pic-upspares.co.uk/
http://autos.bluesock.com/clients/1/site/pages/page_1.php

Answer 2

$3000 to $5000 depending on mileage and if it is ODB1 (95) or OBD2 (96-99).

Easiest route my be to buy a salvage M3 that had rear end damage. Take the engine and anything that you might need during the swap, then part the rest of it out.

Salvage M3's run anywhere from $5-$9000. If you can find one for $5000, take the engine and then sell the rest you might be able to work it out so you are ahead of the price of just buying the engine alone.