Upvote:4
Latvia has several special offer coupon websites and aggregators; to name a few: Zizu, Lieliska Dāvana, Gudriem.lv (an aggregator). You can search “kuponi site:lv” for more, although there’s a good chance the aggregator already shows the same offers. Most of these websites can be viewed in Latvian and Russian but not in English, so I’m afraid you may need to view them through an online translator to make sense of the text. Search “fotosesija” for “photo shoot”.
I have never done such a photo shoot myself, so I am not sure I fully understand what you are looking for. However, I have so far found only a couple outdoor photo shoot offers in central Riga on these websites (and one in Sigulda, a charming town some 50 km from Riga). Most of the other offers seem to be studio shoots. The prices are lower than your quote at €25–€70, but each of them is also advertised to take 1 hour, less time than your 90 minute figure, and no details are given as to what (or how many) attractions will be included in the tour or whether dress changes are included/expected.
I don’t know much about Vilnius, but in Riga and Tallinn, some of the main attractions are located in a relatively small area called the Old Town that used to comprise the actual city centuries ago, and photo shoots seem likely to focus on that area. It is entirely possible to walk straight through the Old Town in much less than an hour, but guided tours tend to take a couple hours. Overall, I’d say it’s plausible to shoot at several main attractions in the Old Town within that time frame. However, if you want to add more outlying locations, you’ll need more time.