I go to the Christ store in Coop St. Annahof, it costs about CHF 15 - whatever that says about my watch...

I have also found this overview, which is a year old but probably not too far off: http://www.mirjamfonti.ch/Uhrenbatterie.pdf

Frankly, anything above 30chf is usurious. Replacing the battery is trivial and shouldn't take more than a minute, two at most, and the battery itself is just a few chuff.

Did you consider DIY?

Order by mail, battery (costs 0.50-8chf, probably 3 or 5chf) plus "Uhrmacherset" (7-20CHF, probably 10chf), 8chf postage (all prices from pearl.ch), the tally seems unlikely to exceed 25chf. Or pick up the items in Spreitenbach and save the postage. Next change will be necessary in a few years, at which point all you'll need is a new battery that costs 3 or 5chf.

Make sure you know what you actually need, plenty videos on youtube that tell you. You probably won't need to open the bracelet so no tool necessary. The user manual for your model available on this page tells you what battery make you need.

For Tom's Tissot Touch watch, about Chf 100.-- is a little high, but it's not just a simple battery change.

They need to replace the seals for water resistance and check the functions all work and so it is a little more expensive although shouldn't be this much, around Chf 40-50 would be fair in a Tissot dealership.

It is feasible to do it yourself, but not easy in this watch. The battery costs a little more than Chf 2.-- as it is special size in a Tissot Touch, but if it is not so easy to ensure it is still waterproof, until it's too late.....

If it's a decent watch it is worth getting it done properly.
I took my Tissot to somewhere cheap. In fairness they did warn me that they couldn't replace the waterproof seals. I didn't think that mattered so I went ahead. A few months later the watch got wet in the rain and stopped working. I took it to a watch repairer and was told it would cost more to repair than to buy a new one.

Next time mine needs a new battery - I'll send it away for a Tissot service too but I was really quite careful with the seals when I did it myself and it's been fine for something like a year now since I changed it.

No it's not. Mine used a bog-standard CR1632. It's 1.50 CHF from here in Switzerland.