I'm using a Canon 430EX II with a 6D camera. Can I use the flash as a slave with the Yongnuo YN-622C-TX without any transceiver attached to the flash? I'm really looking for the cheapest solution to use the high sync option of the flash wirelessly. Any advice is appreciated.
No. The 430EXII does not have a built-in receiver for the radio signals the YN-622C-TX transmits. You'll need to purchase a YN-622C transceiver to use as a receiver on the foot of the 430EXII.
The only Canon flashes that have radio receivers built in are the 600EX-RT and the 430EX III-RT, and those use the Canon RT system, not the Yongnuo 622 system, so you'd have to go with a YN-E3-RT or other Canon RT master unit instead of the YN-622C-TX; or consider getting a wireless eTTL master unit and use the built-in optical slave in the 430EXII, but you'll have all the range, reliability, and line-of-sight issues of an optical system.
Alternatively, you could purchase a YN-685 flash, which has a YN-622C receiver built-in, instead of using a 430EXII. It's more expensive, and a big unit (larger than a 580EXII), but more convenient, since you don't have to pack the trigger and its batteries--just the flash.
But getting a $40 YN-622C transceiver is probably the cheapest route.
No. The Yongnuo YN622C-TX is a radio transmitter. The built in receiver in the 430EX II is an optical receiver. The two are not compatible without a radio receiver YN622C on the 430EX II. The YN622C runs about $35-40.
Your other budget option is to use a 90EX as a master flash to control the 430EX II. They go for around $45 on eBay. But the small size and guide number of the 90EX means the range will be somewhat limited, especially outside in bright light. The 90EX is marketed as a compact flash for the EOS M series of cameras, but it will control any slave flash compatible with the Canon E-TTL wireless optical system. This includes HSS functionality.
You will need to have a YN622C tranciever attached to the 430EX II.