Realistically, you'd be looking at a soho (small office/home office) load balancing router, specifically a dual-wan router. Cisco offers some [1] as well as Peplink [2]. I don't have a lot of experience with them (did some research on it a few years ago but never pulled the trigger), so YMMV when it comes to custom firmware etc. Doing a google search on "dual wan router" would give you a good feel for the environment. It's possible to find them under $200USD. $350 isn't entirely out of the question depending on the features you're looking for.
If you're outside of the US (I'm guessing, based on the speed of your link), some products are export-restricted. You'd have to check on support for your locale. Another option if you're in a DIY mood is making a custom Linux box using split access features of iptables [3].
If you don't want to mess with iptables, ClearOS (CentOS derivative) [1] has built-in multi-WAN support [2], including auto-failover and load balancing. There's a GUI, but you can always SSH in and configure things manually.
My home router/server is a MicroATX box with an Atom D525, 4GB RAM, 2 x 1TB RAID-1, and 2 x Gigabit NIC. Cost a few hundred dollars to build, draws ~16W idle, and is almost silent. DNS, SSH, FTP, SMB, POP/IMAP, SMTP, QoS, PPTP/OpenVPN/IPsec, and dmcrypt are included. The Atom chip is fine for home use, move up to an Athlon if you're pushing a lot of SSH traffic.
If you're outside of the US (I'm guessing, based on the speed of your link), some products are export-restricted. You'd have to check on support for your locale. Another option if you're in a DIY mood is making a custom Linux box using split access features of iptables [3].
[1] http://www.newegg.com/Product/Product.aspx?Item=N82E16833124...
[2] http://www.peplink.com/
[3] http://lartc.org/howto/lartc.rpdb.multiple-links.html