Have a look into vintage lenses. There are downfalls obviously (needing adaptors, losing autofocus, etc), but some of them are really quite fantastic lenses for really low prices. And, as they were made in an era without autofocussing, the manual focus on them is a lot nicer than a number of lenses today. The build quality is really nice as well.
http://vintagelensesforvideo.com/ is a useful website. It's pretty new, so doesn't have a heap of information, but it's a nice resource nonetheless.
You would be able to get a nice 28mm, 35mm and 50mm in your budget, and still have a bit of cash to throw around.
Although, if you need autofocus (I see you do photography), they mightn't be ideal. They also have a bit of a different look, which you might no like. And sometimes they can come in not-so-flash condition (to avoid this, ask questions on ebay, read the descriptions carefully - and if they're a dishonest seller, report them/lodge a claim for a refund). They also don't come that wide, as they are designed for full framed cameras, so if you do need something that wide, you may want to get something modern. I think zoom is relatively useless, but if you like documentary, then it may be of use to you (it also makes things a little more versatile in tight situations).
However, here is a few suggestions with how you could spread your budget using just primes
Lets say you want the 14mm Rokinon - based on the value the last two sold on eBay for, you can pick one up for around $280-$300 (although all current prices are a bit higher, so you might need to wait a bit for a good deal). I selected the 14mm, because it's going to be the hardest to cover with vintage primes
This gives you around $200 to play with.
The incredibly popular vintage Helios 44-m 58mm is $20-$30 (you can sometimes pick them up even cheaper). It's an odd focal length but a really nice lens (test of it on a 60d
https://vimeo.com/26729587 - bare in mine this has had some grading)
The Miranda 28mm sells for around $20-$50 (this is about a 50mm equiv on your crop sensor) (
http://www.youtube.com/watch?v=_x96YgeG8s4 the miranda on a t3i)
you still have $100-$150 to play with.
You probably want something between your 28mm and your 58mm.
I would suggest a 35mm, or maybe a 40mm. Probably a 40mm, because it's more in the middle of the two focal lengths.
At 40mm, there is the Konica Hexanon f1.8 which sells at about $20-$50 (
https://vimeo.com/42406396)
At 35mm, you could try the Fujian 35mm (around $30) (
https://vimeo.com/61456890). This lens has quite a specific look (partly because is not at all sharp at the edges). I don't currently have a 35mm, but may get this for a flashback sequence due to this look.
This comes in at
$350 - $460
There are, of course, plenty more options. The Asahi Super-Takumar lenses are very popular, the Tamron (
https://vimeo.com/65788669) and Vivitar 28mm's (
https://vimeo.com/17350203) fare well, and of course, if you need to get longer focal lengths, there are a number of options there too. It really depends what filmmaking you want to be doing, what your style is, and what focal lengths you want covered.
Remember; whilst having great lenses will help your final product, it won't make you a better filmmaker. If you are a rubbish film maker with a $500 lens, a good film maker with a $50 vintage lens will produce images that far exceed yours.
