I find that geothermal does not work well with radiators, and will require a back up heat source. Ensure the geothermal is sized correctly to suit the installation and then work out the running costs. Many are under-sized to bring down a) the installation cost and b) the running cost. The result is underheated house for a greater running cost.
Your estimate for installing a condensing boiler is pretty much on the mark and that should include, commissioning, etc.
My advice is to not rush into the decision. It is worth delaying until you know/research all the facts and then make an informed decision. Speak to homeowners who have both and compare.
Will the extra money be re-couped within the lifespan of the unit or will you have to replace major parts? How much will it cost to replace compressors, motors, etc. with the geothermal. What is their lifespan? You should be asking any supplier/installer these questions and not get a sales pitch answer.
There are plenty of posts of AAM regarding both, so a little research is called for.