Transmitters are a very personal subject, for quad flying you are going to want an OpenTX transmitter. Currently those are made by FRsky and Jumper. If your FRsky doesn’t do D8 you need to add an XM+ or similar micro receiver onto the quad, it’s easy and range is usually much better. If you switch your quad to D16 you can bind to any of the non D8 transmitters, most of the V3 Toothpick boards allow D16, but not all. Some older pre built ones will only have D8 available. Check your instructions.
You have, in rough price order,
Taranis X9 Lite- DOESN'T do D8
Second hand QX7- Old ones have D8.
Jumper T12
Out of stock lots of places
Taranis X9D - second hand, old ones do D8
FRsky X Lite- Batwing controller.
Jumper T16- Does everything a much more expensive radio does.
QX7- New pro version is as much as a T16. No D8 on 2020 one.
Taranis X9D 2019- No D8.
Jumper radios come with a multi protocol module, which can bind to almost every manufacture’s receivers, it has all the common and toy ones on. They also allow you to run TBS crossfire modules with no mods or software changes. IMO the T16 Pro is the best value radio to buy new. The T12 pro is $110 ish and has everything the QX7 pro has plus the multi protocol module but it’s out of stock everywhere. Only downside of the T16 is no battery included.
A second hand TX is a great idea, my X9D plus was $130 in mint condition with battery pack, charger and hard case. Beat up QX7 sets can be had for $60, if a switch or gimabal is damaged those are fairly easy to swap. The X9 Lite is good but you have to get compatible receivers and it doesn’t have a full size module bay.