Hi @jenna, looks like there’s some good advice in the thread above, so definitely check it out if you haven’t already! 🙂
I would not be afraid of buying a tripod used from an online marketplace as long as you can look it over to make sure it’s what was advertised. You’re much more likely to get a good quality tripod for a better price by buying used, so I would definitely go that route. I bought an old Bogen (made by Manfrotto) tripod off of eBay for less than $50 I think, and it’s as solid as a rock. Kinda heavy like a rock too. 🙂 Something like this one: https://www.ebay.com/itm/226220472584
It came with a Manfrotto 3265 pistol grip head which I really like!
Yes, you can buy just the legs and add a head from somewhere else as long as they use the standard connections. (3/8-16 screw to attach the head to the legs) I have a video head and a pistol grip head for my tripod, and I switch them out all the time.