bol.com has them.
I checked the price of Sword & Shield Battle Styles Booster Packs, which are around 9 euros.
I checked the same booster on nedgame and they sell it for 6,99 (which is probably the normal price).
I checked the corresponding booster box: nedgame is out of stock, bol.com has it for 136 euros. There's 36 booster packs in a booster box so that's roughly 3.7 euros a pack.
I'd recommend just checking the prices between the two and see which is cheaper, as both tend to adjust their prices randomly. nedgame is often cheaper, but not always.
I have used both sites for various merchandise, but I'll admit I don't collect the Pokemon TCG myself.
This is just online though. You should also check your local stores to see how much they sell booster packs for. They may or may not be cheaper.
So basically only tip I can give you is compare prices regularly when buying online, as they tend to be adjusted xD
Also Hello and Welcome Kevin!