The short answer
Wedding guest photo sharing costs anywhere from free to €600 or more. Free shared albums (Google Photos, WhatsApp) cost nothing but lose photos and have no live screen. Dedicated apps priced per event cost €39 to €79 for the whole wedding. Hired photo booths cost €300 to €600 or more for a few hours.
The three ways to collect guest photos, and what each costs
There are broadly three approaches, at very different price points and with very different results.
Free shared albums (€0)
A WhatsApp group or shared Google Photos link costs nothing. The trade off: low participation, photos trickling in for weeks, no live screen, no highlight film, and a real chance images get lost in chat history.
Apps priced per event (€39 to €79)
A dedicated tool like Forever Wedding charges once per wedding: €39 for Basic, €79 for Premium, with unlimited photos, a live reception screen, a highlight film and at least a year of gallery access. No monthly subscription and no cost per photo.
Hired photo booths (€300 to €600 or more)
A physical booth or printer hired for the evening. Great for printed strips, but limited to one location, a few hours and a queue, so you do not get coverage of the whole day from every angle.