Total: $700. SSD is optional, but I never use my old sata hardrives anymore. I would rather do with less storage space. If your board works well in sleep mode, then you may not need an ssd. Some of my newer boards don't power up properly in sleep mode due to bios options or wireless keyboard/mouse issues.
Not if you don't download much and turn off your pc instead of using sleep mode. Booting up with a full load of windows 7 security files is slow without the ssd. It's still the main advantage. It's also quiet. This poster has a limited budget, so it's up to him to estimate his space requirements and decide if he wants a better case or motherboard instead of the ssd.
Downloading is hardly relevant because that's bottle-necked by internet speeds, not storage speed. Booting up on a 7.2KRPM HDD or better isn't going to break any records, but you only do it no more than a few times a day and it's not bad. All the time that you are on, you are loading other stuff and that makes a far greater difference than the mere boot speed does.
Sure, it's OP's call, but an SSD is most certainly more important for much more than mere boot speed.