We own a vacation rental property in Garrett County, Maryland. It's a 4 season type rental area with ski slopes for winter, mud in the spring, the lake in the summer and hiking / leaf peeping in the fall.
House access - We have a programmable keypad that we use for access, so we don't have to bother with keys. Then, if 2 or 3 families are renting, they don't have to worry about who has the keys. We change the code regularly. There are also WiFi enabled keypads you can use.
Rental agency - We rent on VRBO and Homeaway and I send out contracts and use the homeaway lease feature. Previously, I used paypal and sent out leases myself. I hated paying 8% and/or a per lease processing fee to someone else. $1000 / year
County registration fee as a transient vacation rental and health department fee - $350 / 2 years plus annual $70 well check
Maintenance / cleaning - We have a local maintenance guy we can call; he also plows our road, so he is basically in town all winter and typically in summer also. For cleaning, we started with an agency for the first year and got to know the cleaning company then switched to going directly to them instead of using the agency. They keep a good eye on the place, too.
Unexpected costs - FUEL! Our furnace burns kerosene and is EXPENSIVE! Our first winter it was about $300 / month for weekends only. Definitely not part of our budgeting / cash flow estimations! We installed a wireless thermostat, so now we can keep a better eye on the local temperature and ensure nobody forgot to turn it off after their lease was up and the place had been cleaned. But it's still more than double what we pay for where we live full time!
Snow plowing - again, beyond our wildest budget line imaginings. Our first winter it snowed maybe 20 feet or so?? The house is on a dirt road with other houses, but both the road and the driveway have to stay plowed and keep cinders on it in winter since it is north-facing (ice).
CABLE / INTERNET - at our personal home, we cut the cable cord over 2 years ago to become more Mustachian. We pay < $80 / month for very high speed internet (we are a household of 7 people with an au pair). But since this is a vacation rental, I haven't felt comfortable going purely Netflix since some people are more "dependent" on their TV than we are. Even with negotiating every year for a better rate, we still pay almost $180 / month for internet and cable TV. That's a big $$ item to affect cash flow.
Replacement towels / furniture / bedding - it's been fairly consistent for the last 4.5 years, but we estimate about $1500 year for an annual furnace inspection, replacing sheets/towels (sleeps 18 people), broken dishes, paper products, etc and another $600 for random things (replacing DVDs, new alarm clocks, light bulbs, new outdoor chairs for firepit).
Occupancy rate - since it's transient vacation rentals from 2 to 7 days, we have never had more than a 50% occupancy rate. ranging between 135 and 180 days per year. And up to 50 separate contracts.
Having said that, we also enjoy it for a ski weekend and a partial week or two during summer or fall, so it's been a great investment for us. And our plan is long-term. But it took 4 years and additional $50k investment (increasing from 3 bedrooms to 5 bedrooms) to see a positive cash flow.
Good luck with your decision!!