I've done mini sessions in two ways.
The first is as a fundraiser for rescue at a location where folks all come on one day. The second is as a coupon deal from Wooftastic Wednesday (like Groupon, but from a local dog magazine).
In the first case, I've done as many as 30 sessions in a five hour period. That was way too many and we were totally frazzled. 4-5 an hour is a nice average, but unless we take appointments we normally end up with a rush at the start time and a rush near the end time. We have one of these on 19 Nov this year for a group we've worked with for several years now. We're charging $40 for the session and giving $20 back to the group, prints purchased separately. This will be our fourth year doing this for this group and we've never done fewer than 15 sessions. Of all those clients, only one has ever converted to a regular, private session client.
We offer packages specially designed for these events. The contents of each package have changed each year, but what we've found works best is one basic package, a mid range package price just above it, a higher end package, and a "yeah, right, nobody will buy that" package.
These are not money makers really. We average $400 in session fees (our take) and a $400 donation to the rescue. Most clients purchase the mid-range package with a few on either side of that. We started offering the "nobody will buy it package" after our second year, and out of all these events for this group and others we've sold three of them. We price it in the $300 range.
This year, we're trying something new. Each mini-session client gets a postcard offering $150 off a private session, plus an additional $100 donation to the rescue. We put 200 of those in the goody bags at our last event (18 Sep) and haven't had any takers yet.
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The coupon deal is ongoing. We offered a $49 mini session with one 8x10 or one digital file included. All other prints are offered at my regular private session prices. We sold 27 with an expiration date of 15 Dec and mandatory "expedited processing fee" after 15 November. So far, 16 have booked their appointments and nine of those have been to the studio for their session. One upgraded to a regular session by paying the difference.
Of the nine sessions conducted, only two have placed their order, they each selected only the included digital file. The one who upgraded to the full session makes the campaign a success.
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For reference, my private sessions are $350 (I frequently have $100 or $150 off offers out and about) and average print sales run about $1200 so one session plus print sales has the potential to out-perform an entire event with a lot less work.
We're trying to transition to our fund-raisers being $150 off a regular session with $100 back to the rescue and done at the studio. We don't get inundated all at once, but four sessions make as much for us, and for the rescue, as a whole day event before any print sales are even considered.
Forgive the rambling, but I hope that helps.