You'll need a filter and a heater (duh), but most kits don't include a heater. If it were me, I'd buy the tank on it's own, and buy your filter and heater separately so you get to pick which ones you want. Most of the included filters in kits are pretty bad (Top Fin aren't horrible, but almost all of the Tetra filters I've had break in a few months).
If you have access to Amazon, I would recommend just ordering some "add on" items if you have that option. I just got the whisper 10 for like $4, and there are some good heaters for $10-15, there's good siliconeairline tubing for $4-7, a check valve is basically a dollar or less, and I'm sure there are sponge filters too. And I think Petco's dollar per gallon sale is still going on, so you could grab a tank for ten. I say try a couple of different websites and compare prices for individual parts vs the kit.
For a small tank like 10 I'd just buy the kit. This will give you the tank, the light, the hood, and a filter. To buy the tank alone is like $23 then the hood $24, then the filter etc, it all adds up. A kit is like $25.
If you are looking just to house a betta, you can get a decent kit and just add a heater. The included filter with our 10 gallon kit is not very strong, but it should do for a single betta. I think it’s much more expensive to get all the components for a 10 gallon separately. We have one 10 gallon kit, and two basically free 10 gallon tanks on their own. It’s costing me more money to find all the accessories separately (canopy, lights, thermometer, heater, filter) for the 10 gallon than it was for the 10 gallon kit on sale. For larger tanks that’ll be home to more/bigger/messier fish, you’ll want to customize your equipment as you’ll most likely need at least a more powerful filter.
Sorry, just to add, we have the Marina 10 gallon kit with LED lights. I’m very happy with it. The filter is good quality, just low gph.