Based on you reply, the SNA5000 family would not suffice to your requirements as it does not support frequency offset measurements.
Nevertheless, of your hart is set on Siglent than my answer might be in vain altogether.
Baseline: SNA5002A(4.5GHz) for $8,499:
https://www.tequipment.net/Siglent/SNA5002A/Network-Analyzer/?search=trueSweep: 150us/point fully called 2 port
Dyn,. range: 125dB (30MHz to 4.5GHz)
Noise fl.:-125dBm/Hz
In your price and frequency range there are a few alternative options:
Tek TTR503(3GHz) for $6,000: Slow sweep speed, no offset freq. options, similar performance to SNA
https://www.tek.com/datasheet/vector-network-analyzersPico VNA 106(6GHz) for $6,500: 185us/point fully called, no offset freq. option, has AM to PM measurement, lower performance than SNA
https://www.tequipment.net/Pico/VNA-106/Network-Analyzer/?b=y&v=99940#descriptionCopper Mountain M5045(4.5GHz) for $7,895: 70us/point fully called, no offset freq. option, has AM to PM measurement, higher performance than SNA
https://online.fliphtml5.com/pbaab/xzks/#p=13Copper mountain S5054(4.5GHz) for $10,995.00: The same as the M5045 with added frequency offset capabilities.
At the end of the day, if all you want to do is learn and do basic measurements with reasonable accuracy, than a LibreVNA or NanoVNA might be a much smarter way to spend your hard earned cash

LibreVNA:
https://www.amazon.com/Analyzer-AURSINC-100KHz-6GHz-Measuring-Parameters/dp/B092Q6W2Z6NanoVNA:
https://nanorfe.com/nanovna-v2.htmlWhen looking at VNA data, there is a lot to compare, I did a VERY rough comparison. The trace noise, dynamic range, uncertainties, calibrated/uncalibrated directivity etc. are all very important when doing precise measurements.
Making sure to check the resBW at which each company specifies their parameters so you compare apples to apples is very important.
If you want to do PA measurements, the Output power range is important together with its accuracy specifications.
Hopefully this helped a bit

Personally I would go with Copper mountain for 2 ports.