I found it varies a lot from car to car and who maps it. My old Saab 9000 came with a pro tune from Maptun with a stage 3 remap which I got told cost over £500 back then including a live mapping session, I had it remapped again by post to stages 4, 5 & 6 for less than £100 each time via a home tuner (best UK Saab tuner imo but he's done a lot of r&d improving the maps) the previous 9-3 also got remapped the same way via T5 Suite to stage 1. On these cars stage 1-3 are more or less generic maps so not much difference between them as tyres no real hardware changes bar a 3" DP. So nobody really uses pro tuners here as its miles cheaper to get the guys on the forums to remap either by post or take a drive to their homes and get it done there. So you can get t5, t7 & t8 cars remapped for under £100 each!! Some massive gains to be had as well, my lpt 9-3 went from 154bhp to 220
really good bang per buck factor
This 9-3 has a few different mapping options though and none as cheap as it's the v6, all seem to be around the same price at £450 give or take. Mine was done via email from the states, just plugged the supplied iFlash dongle into the obd2 port & laptop, pressed a few buttons and 5 mins later it was done. Nice & easy. The older saabs I had to buy a spare ECU then send it off to get done.
Also additional maps are free (with JZW) even if I go for more power so the £450 was worth every penny, so handy now as I'll need to remap it a couple more times this year for the bigger turbo and bigger injectors and again for its final stage 5 tun, but some charge around £100 for additional maps or some cases a lot more. I also get 3 or 4 different maps to upload at different stages of tune so it's pretty decent value!
Plus there seems to be a huge difference in performance gains between tuners. JZW & Vtuner gets massive torque from a stage 1 map, similar bhp to the rest but the extra torque is huge! Comes at a cost though as the standard clutch is pretty much clinging onto life here, so tunes like Maptun & Hirsch are a lot more conservative (but still quick!!) they seem to be more linear in power delivery where the JZW tune gives loads more oomph lower down but starts easing off around 4.5k guess it depends what people prefer.
Great fun though