The Jolly Logger is right... it's kind of like asking 'how much to paint my house? It's a big house". Any estimates will be vague at best.
The devil is in the details, and there are a lot missing. The distance to the dump, the size of the truck, and how much you are paying to dump for example, and the spread of the trees. Are the 4 oaks that are getting trimmed in addition to the rest of the trees mentioned? Are they all tall narrow trees like pin oaks, or huge spreading trees like english oaks which may spread out a couple hundred feet... Also, the numbers you've given on the trees don't quite match up, 75' high and only 10" in diameter?
Anyways, working with what we've got, the way to get it done is with a truck with a chip bin and a chipper. All those smaller trees you can knock straight over, and winch as whole trees to the chipper. 15-20 minutes each tree, all gone. The church may even take the mulch. If you've got to drop, limb, buck, load, drive and pay to dump then bank on closer to a day for each tree, or for each two trees depending on how far to the dump. You can fit approximately 10~15 times as much trees into a truck by chipping brush as you can by loading it loose. The oaks aren't especially large, but assuming they're pin oaks you'd be looking at knocking the whole job over from go to stop in 2-3 days with a small crew and a truck and chipper. $4k at the very low end right up to maybe $6.5~$7k if they're bigger trees. Stumps sound like they're worth about $800~$1000 on top. I'd outsource the stumps if it was me, someone with a good size machine can knock that out in a half day or so. The size of machine you're likely to be able to hire will take several days and still not do as good of a job.
If I was in your position, I'd be trying to eliminate as many variables as I could. Eliminate dumping fees for starters, forget the lift (not sure why you mentioned that in the first post if they can all be dropped) Assuming again, that your stepfather is a competent faller and has enough saws and plenty of chain, have him drop all the trees on the first day if there's room. Have 3-4 guys there on the second day, see if you can hire a chipper. Get at least a 12". Bank on hiring the chipper for 2 days but you might get away with one, especially if there is plenty of room on the site. See if the church will take the mulch - you may not even need a dump that way. Third or fourth day buck up all the bigger trees, Hire the bobcat for a day and take the oak back to your place where you can split and stack at your leisure and make some money off the firewood if you're so inclined. Otherwise, you shouldn't have too much trouble giving it away to any local firewood guy. He might even come pick it up if you load him with the bobcat. Sub the stumps out, and leave a whole day for cleanup if they require it - all the noodles, leaves, etc. It will easily fill a small dump truck, maybe even two loads.
If the other people bidding are tree guys they'll probably come in under you though if you've got to hire all that gear honestly. And If I was the client I'd be hiring them anyhow - they're licensed, insured and experienced. A tree company with a 20 cube truck and an 18 inch chipper with a winch and a small crew could bowl that job over pretty easily from how you describe it.
Shaun