Do you need UltraScale(+)? The Tang Mega 138k has way fewer LUTs than most US+ chips, it's a completely different class of FPGA.
You can purchase a SQRL FK33 (VU33P on PCIE cards) for $250 used in the Dream escrow Discord. Here's one on eBay for $400 (a little steep) - this is the cheapest you will get into UltraScale+: https://www.ebay.com/itm/387229340513 This is also the cheapest way to obtain 8GB of HBM, which you will want for a GPU eventually.
For $1000ish, you can get a C1100 (VU35P, 2x the area of VU33P, 8GB HBM) - https://www.ebay.com/itm/186414684753 - these do not require a Vivado license.
I definitely do not need a very large FPGA, though navigating this space as a newbie is quite hard -- I've built some small projects (serial multiplexer and a WASM CPU) on the Tang Nano 9k/20k
I think the difference between a $220 board and a $1000~ board is quite large for a hobby project
Bigger is better here - even if you don't use the LUTs/FFs, the tools have a much easier time placing/routing a relatively small design into a huge chip.
If your budget is $220ish, I would buy a used FK33 without a doubt for $250. You can use the Vivado trial (and keep renewing it.)
439680 LUTs, 879360 FFs, 672 BRAM, 2880 DSP, 320 URAM, 8GB HBM is plenty to work with.
The FK33 also has an FTDI chip onboard for convenient JTAG flashing, comms, and management.
> though navigating this space as a newbie is quite hard
This space is all about the tools: Xilinx is head and shoulders above everyone else. Quartus might be second, Lattice's tools are absolutely terrible (but open-source workflows exist for some of their chips.)
If you're designing PCIe devices and not wanting to build the PCIe IP, Xilinx's is absolutely the best in that department as well. There are more PCIe examples and boards for Xilinx chips than probably every other manufacturer.
For making a product with UltraScale+, you do not need a dev kit.
You may use e.g. the KRIA K24 SOM ($250) or the KRIA K26 SOM ($325) (the sizes of the FPGAs differ for these variants).
For designing a product with these SOMs, you can buy a few cheap development boards (the development boards including a SOM are cheaper than the SOM bought separately, so obviously they cannot be bought in big quantities) like the Kria KD240 Drives Starter Kit or the Kria KV260 Vision AI Starter Kit or the Kria KR260 Robotics Starter Kit.
You may buy these SOMs as single units at higher prices or as hundreds at discounted prices at many distributors.
These SOMs include 2 GB or 4 GB DRAM memory, QSPI or eMMC flash memory and some interfaces, like USB 3, Ethernet, PCIe Gen2 x4, transceivers suitable for HDMI 2.0 and DisplayPort 1.4 etc. and the FPGAs include quadruple Cortex-A53 + double Cortex-R5 cores, which can initialize the FPGA or reconfigure it remotely whenever desired and which can run a Linux OS. The FPGA also includes a Video Codec Unit, but that is limited to an aggregated resolution of 4kp60 (i.e. either a single 4k stream or up to 32 lower resolution streams), and also a Mali GPU and a (slow) DisplayPort controller that can be used as the video output for the operating system run on the Arm cores.
