Agreeing to pay a "small fee" doesn't make make an SD "serious" IMHO, what it does is prove to the POT SB that SHE is "in charge" and it just sets the wrong tone to start the relationship.
It's not a matter of being cheap, I don't do "coffee" dates, I prefer dinner, or at least drinks and I don't mind at all if we "run up the tab" to way more than the $20-50 that you are talking about, but what I won't do is give any kind of "allowance" to a woman I am not sleeping with. I don't mind having several dates with a woman before going BCD with her, but I am not going to be paying her simply for her company, no more than I am going to pay a hooker for "time and companionship".
I know you are going to have a hard time believing this coming from a self admitted oink oink man like myself, but I am actually ok with going out with women where I know we are never going to be anything more than friends, but I don't pay my "friends" to hang out with me.
BTW SB's outnumber SD's by a factor of several to one on SA, IMHO it's more incumbent on her to prove that she is "serious" than it is for me to prove the same to her. My time is much more valuable than any twenty something year old POT SB, not to mention I am springing for dinner, drinks or whatever so the only "risk" she is taking is the risk of accepting a free dinner from some guy she ends up not being interested in. One other thing to keep in mind. I might be a pig, but I am a pig with standards and hot pics don't guarantee a hot woman is actually going to be who shows up. If a hooker or an SB who expects to be paid for her "time" shows up not looking like her pics, I am going to turn around and walk without leaving a nickel. OTOH, if a POT shows up a little chubby or not as attractive as her pics and I decide that I don't want to have sex with her, I am still going to go through with the date and buy her dinner or a few drinks before parting ways. I would not be so magnanimous if she was expecting to get paid too.