I'd questioned continuing in this and becoming another one of "too many cooks" but it's starting to go off the deep end. I'll guess Jason isn't interested in SPLITTING HAIRS. Rather, just wants something affordable to suit his needs!
How long will you keep the system? If not more than 3-years, then don't worry about what could be needed...get it later. A good QUALITY board, like ASUS P8Z77-M, has (2) SATA 6Gb/s and (2) USB 3.0 ports. Somewhat over your target $100, but Core i5-3570K option SAVES you nearly $20, unless that SERVER Xeon is really necessary...?
Be aware the ASUS B85-PLUS board uses LGA1150 (4th Generation Core/Pentium/Celeron) and is full-size ATX. Are 3-extra PCI slots even needed? It does have (4) SATA III 6Gb/s ports; although by the time you'd buy a third SSD, you could add a PCIe card, or may even decide to get another board. Real SPEED is/will be from a PCIe SSD anyway.
Points to ponder:
1) Only consider overbuying features/specs if you'll keep system for 5, 7, even 10 years. Apparently many (at least 'enthusiasts' on forums) don't do that anymore.
2) Unless you're a REAL professional using specialized (perhaps rigged to underperform with anything but Intel) software and/or NEED absolute maximum performance (aka: a money box) AMD is a GREAT option to get the MOST value for LEAST cost and performance SHOULD be plenty...IF your (audio) software works okay. That I don't know & those who do (if any) haven't spoken up here.
3) Two GREAT choices have been given for ASUS P8Z77-M and ASUS HD7750-DCSL-1GD5 (by CA_Steve) and he seems well-versed in DAWs. If AMD is out for you, go with those; or hem and haw until you're more confused than you started
4) Excepting URGENT need, you can always wait for sales, prices going down, or budget to increase. Don't waste time on cheap boards, or buy JUNK that saves only a few bucks! Just NOT worth the pain, IMO of course...it's your money.
Unlike MANY forums (most) people at SPCR really do want to help, even if it gets unfocused sometimes :p I've now written over 4 articles for this guy (3 PMs and no, he didn't ask) so enough from me