Myrna,
As someone who used to work as a hiring manager for a number of small corporations, and as someone who never tolerated a sexist wage gap for even a day:
rule 1: Come to those meetings with solutions not problems.
Acknowledge that no one will come away with everything they want, but the common ground is possible and you are united by a common goal: keep the good work happening and everyone making good money.
Make THEM do the research, (and agree to continue the negotiation at a meeting in less than one week). This is to accomplish two things: a. give them a chance, one, to avoid getting called on the mat in front of everyone for being a sexist idiot for paying you so low and b. it gets to be "their idea" that they should bring your wage in line.
www.careerbuilder.com and www.monster.com both have good salary calculators.
remind them NOT that you are willing to quit or find well-paying gigs elsewhere (this bluff doesn't sound like it's true anyway), instead remind them that anyone else coming into the company, any new recruit worth a damn, would be aware of the research on Monster/Careerbuilder and be unwilling to work for such a low wage as what they've gotten away with so far.
spin your low wage as a calculated leverage plan AND company loyalty thing on your part: you accepted the responsibilities so you could show your worth and the risk/cost would be all on you. You did your part, and made them a lot of money in the process, now it's their turn to do theirs for the upcoming year(s).
Have the hard numbers to back the above up: if you come in showing how turnover stopped when you took over, and how labor overages dropped, and you've got, say, $50,000 that you've saved them in the last year, then that 25K raise looks like a fawking great bargain.
Tell them what you need the money for. You say here you don't need the money. HUGE mistake. Make something up then. You want to get a house -may be one closer to family (in an expensive neighborhood), you need to help out your aging parents, need to take that trip to europe that was cancelled in high school that you had your heart set on, you want to put your little brother through school, a donation for the new church building for your favorite house of worship - anything worthy of that 10/hour. HR managers will see through your "just practicing" for what it is. You need a Cause, a reason for someone to want to go to bat for you. Too late to lay groundwork in the rumor mill, so just: Lay it on the table now. Make it this huge thing you are just revealing to THEM. Make sure it's not something (like school, having a brood, wanting to partake in deadly X sports) that they'll assume would take you away from them. Something that grounds you to the local scene is best.
Be aware that with the fact that you are supervising several people you have even more value that just YOUR role: if you DO leave, some of them will go too. That's how it works. Do not lay this card on the table as a threat, but allude to it like the salary thing "I know we've built a good team here - I doubt some stranger could keep the momentum that I've created with my guys. There's a chemistry worth more than just time."
Put them on the defensive with questions in the second meeting: "So, what would YOU ask for in this role, for this much responsibility? Either benefits wise or a solid dollar amount?" is a great opener.
And yes, benefits are often MUCH easier for a GM or Dept head to provide than dollars. Benes don't cost hard cash from the same accounting column, so they are essentially "free" budgetwise. Milk these hard. I once got a CEO to double the vacation/PTO package once without blinking an eye "so long as we don't have to pay him more" was all he was worried about. Free company phone? Bigger office? Flexible start time? Comp time? New laptop? Use of the company car? telecommute once/week? These are practically no cost compared to trying to dredge more salary money from a shallow budget.
Socialize the fuck out of the decision makers. Flirt, buy them a beer, talk shop, talk shit, brownnose a little even. Whatever it takes: It counts, (it sucks), it works & it pays off. Never lay it on thick, but be clear you are enthusiastic enough to try and ply them. Come decision time, they'll remember the enthusiasm not the free beer/cleavage.
Value-added communications: in every practical opportunity, always bring them a treat of info... something you read in a trade magazine, some swag from a convention, that sort of thing. Ideally, a money-saving idea. Even if not implemented, the idea and gumption count. I once got a 35% salary jump myself combining this and the "look how much I saved you last year" thing.
You are in a tremendous position of power right now. You owe it to yourself and to all the people who haven't gotten a raise they deserve to nail this. Best of luck