[Hocrest]

It depends on what you can do yourself and where you get the parts.

I've replaced mine with a stock 3.545 tranny out of a junkyard for less than $100 including new seals and fluid. Getting a rebuilt from SOA is going to cost closer to $3000. Getting a 4.44 trans and matching diff from a yard with a warranty is probably closer $500-600. An auto swap at a shop is going to run ~$500 in labor

For an MT swap, if your able to fab your own pedal box, linkage, drive shaft and cross member you can put in a 5 speed out of a early Legacy for under $1000. If you want it to be "bolt-up" you can get the kit from YT for about $1000, find a trans and spend a good weekend + putting it all together. If you plan to abuse it and want something more reliable you're looking at closer to $2000 to get a box out of a newer WRX. If you want it installed for you, check with YT but I think he gets ~$1000 for the swap.