I will offer you what little I do know....
On the app Bumble, you can sign up and swipe right on girls for free. But if you want to reply to a girl's message, you will have to pay the app.
Source: I have talked to guys IRL who have used this particular app.
eHarmony charges both men and women to sign up, so nothing for free (except maybe browsing other users' pics). This info is about 3 years old....
I am unsure about paywalls for Tinder or OKc, so someone else will have to answer for those...
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...what do the public, the great unobservant public, who could hardly tell a weaver by his tooth or a compositor by his left thumb, care about the finer shades of analysis and deduction!