Any other inexpensive PCIe RAID Controller card, fully compatible with ESXi 5.5 with 4 SATA HDDs / RAID 10 support ???
Could you give some details on the server model you have?
Sounds like this is a production machine and not just for testing/lab?
If the server is still under warranty or support contract with DELL I would strongly advise to get a DELL controller.
You may get a used Perc 6/i with BBU for example, this should be available cheap as refurbished/2nd hand, maybe even some of the newer Hxxx models.
Other vendor branded (IBM, HP, Fujitsu etc) LSI controllers should be also avaible for a few bucks 2nd hand.