When comparing, consider the FlexFabric 5700-32XGT-8XG-2QSFP+ Switch at least a 40-port switch (32 10GBase-T plus 8 SFP+) or consider the SG500XG-8F8T an 8-port switch (the number of 10GBase-T capable ports). Comparing just the 10GBase-T capable portcount, I do see your calculation of $326 per port on the HP but I see $534 on the Cisco. Using the portcount of all 10G-capable ports without additional accessories, I see $260 for the HP and your calculation of $267 for the Cisco. When stacking the SG500XG-8F8T, you must sacrifice up to two SFP+ ports.
In addition, the HP has 2 QSFP+ ports which can be treated as an additional 8 10Gb ports with appropriate breakout devices as a QSFP+ to (4) SFP+ direct-attach cable or the 40GBase-SR4 QSFP+ module and an MPO fiber breakout cable.
Being a ComWare-based switch, the HP is not an SMB switch and does not have a lifetime warranty and warrants paying for an annual service contract.