What would you buy for $5k...$10k USD?

What (and if) would you buy if you had $5k ... $10k ... $20k to spend on local AI?

So, I'm a contractor and a solo dev working on some products/saas/apps. Basically I usually run up to three cline/opencode sessions in the same time, long running software engineering tasks, often run out of 128k context, so 256k ctx is prefferable. Pretty much every day for multiple hours so I could burn quite a lot of $ daily on OpenRouter. Fortunately, since Qwen3.8 i rarely need to delegate to larger models like Kimi K3 or MiniMax M3.

Apart from code I often work on confidential documents so a local AI or an approved remote AI is a must.

My current AI setup is:
\- dev server with RTX3090 running Qwen3.8 UD Q4\_K\_XL with 128k ctx q8
\- lab server with 2x RTX3090 + 128gb ram running Qwen3.8 Flash Next with 256k ctx

Both machines are fine to run up to three sessions, one on dev and 2 concurrent 128k ctx tasks on the lab server. The performance i get from the 2x RTX3090 with Qwen3.8 Flash Next is close to a single DGX Spark GB10 (according to numbers).

Soon I may need to run more agents and work with other people so started thinking of an upgrade.

Does it make sense to invest in either a single GB10 machine or two and cluster them to get more space for more context and therefore more concurrent sessions? Would you consider other options?

Any feedback appreciated.