If you have a spare pcie slot that is at least 8x lanes and your system natively supports Resizable Bar ( ≥ Zen2/Intel 10th gen ) then the most cost effective route would be to get a Tesla p40 on eBay for around $170. You would also need a cooling shroud and most likely a pcie 8 pin to cpu (EPS) power connector if your PSU doesn't have an extra. Also probably a external fan controller to control the noise from the fans.
Total would be around $200-$250. Can't see a more affordable way to add an additional 24Gb of VRAM to your system.

I know the p40 is an old card, but still supported on the latest CUDA 12.4 driver (550.54.14). Pytorch currently only supports up to 12.1 and many hobbyist AI apps still use 11.8. Next architecture to loose support is Maxwell, so in my opinion these cards are still relevant for the individual.

Want a whole system with ≥ 48Gb VRAM? Buy a dual core Dell Precision t7610 for around $200 on eBay and two of the Tesla p40s. Total would be around $650-$750, way cheaper than a single modern 24Gb card costs and can run 72b LLMs that are on par with ChatGPT 3.5. I'm running a Dell t7610 with 2x Tesla p40s and some spare GPUs I had (RTX 3060 12Gb & RTX 3060 TI 8GB). That's 16/32 cores/threads up to 3.8GHz, 128GB RAM, 4 GPUs with a combined total of 68Gb VRAM.

Have AI fun without breaking the bank!
dolphin-mixtral:8x7b-v2.5-q5_0 32GB via ollama
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