$300 isn't unreasonable for the hearing, if it's required. All the previous advice is well said, about verifying whether you really fit in the "need a variance" bucket, but if you do, that's a reasonable price for a hearing.
Here's why: Municipalities are strapped for cash, so they've very much gone to a "fee for service" sort of model. That hearing probably requires an hour of preparation for staff, with at least one person, perhaps two. It wouldn't surprise me if the staff planner has a notional "billing rate" of $100/hr or more (salary, heat, light, rent, overheads to support clerical staff, benefits, etc.). If someone has to go out and post notices, do inspections, etc. that just adds to the cost.
Here in Thousand Oaks, it costs $600 for a tower permit for amateur radio, and that's a 50% discount from the cost if you weren't an amateur. (For a small tower.. cell towers are more, of course).
Realistically, they figure that's reasonable in the context of a construction job that is in the $10k range (assuming you bought new tower and gear, and paid someone to install it). That's what building permits for ANY sort of construction run these days. It's over $100 to get an electrical permit to run another branch circuit, and when I asked why, they showed me the actual costs of doing it. They have to record this, and record that, and have 2 or 3 different people review it, not to mention the inspector coming out and doing the inspection. Then, there's the proportionate cost of maintaining the records, etc. (Sometimes, I think the frenzy for allocation of costs adds more than the actual cost being allocated.. like hospitals charging for each ibuprofen tablet individually)
Planning has to review it in terms of whether your proposed work fits within the zoning, building and safety has to review it to see whether it's safe. For run of the mill stuff, there's a blanket approvals, but still, someone has to make the official determination that it's run of the mill, and that has to be documented somewhere so that if someone complains 10 years from now, they can say, "yep, we reviewed it"
You might think all the reviews are excessive, but hey, that's the way the laws read (in general, passed by initiative). Someone does something spectacularly egregious, public outcry says "we're never going to let that happen again, let's impose a review requirement".
Most people getting work done aren't aware of it, because it's just part of the contractor's bid; they gripe about the overall high cost of construction in general.