You’d almost have to piece together something like that. Nothing out there will have your requirements for less and $700 ready to go. You might get lucky with searching eBay.
That is a hard ask. It has to do with the number of PCI lanes the CPU has (which is only 9 in total, and they are PCI 3.0 not 4.0). Each SFP+ port requires 4 lanes to operate at full speed. So either 8 lanes in total to the two SFP+ NICs OR the NICs won’t operate at full speed. A SATA controller will need 1-2 lanes depending on how many ports. Each NVME drive will need between 1 and 4 lanes. If you have a wireless card, that is another PCI lane. There’s just no reasonable way to configure an N100 with everything you want. You really need something with a U300 CPU or even a pentium 8505 CPU, which would give you 20 PCI lanes.
Alternatively there are embedded Ryzen chips that have lower TDPs, (V2000/V3000) that have plenty of PCI lanes as well.
I built a 10gbe router using an Asrock Industrial IMB-V2000M board that I picked up on Ebay for $150. I stuck an Intel X520 dual SFP+ nic into it plus it has two realtek NICs built into the board. But it runs a little hot for a 1U case I think. I have it in a HTPC case that is somewhere between 1U and 2U.
There is nothing rack mounted that I can suggest that doesn’t cost over $1000usd.
What I will suggest is that maybe something like an HP T740 with an Intel x520 card would work, if possible I’d go with an x710 card which is a better match. You can get 4xSFP+ in an x710 card if you want to spend the money. But, unless you buy all of this used, you are going to be over $1000usd.
Here is 1 premade firewall that will fit on a 1u shelf and have SFP+ ports:
You could then (probably) install your OS of choice. The 2752 and 2770 would be better for installing in a rack, but more money. I’m sure Netgate has similar products in similar price ranges.
You can also look around for a Supermicro 1u server and add an x710 dual or quad port card, but I bet you are again over $1000usd. Anything in the x11 or newer generation will work, just a little Xeon E3 with 4c/8t should do what you need. I’m currently running an X11 based Supermicro with a low power Xeon E3-12xx and a quad i350 card for my firewall, plenty for what I need right now. Dual boot drives in a mirror and 16GB of ECC RAM (because the board requires ECC RAM).