Tight budget and a big room... ~3600'3?
The Sub is going to be a sink for your budget, but in all honesty... consider shopping for the best single sub you can allow yourself to afford. Then down the road, add a second matching sub... and then maybe a third.
Other than that... what are your goals with this? In terms of audio... are you wanting to build to a high end system? If that's the case,
@everettT has it. Start with just two small bookshelves that you can repurpose as Surrounds down the road.
You likely won't find them in stores, but SVS Primes could be a place to start... maybe not ideal as wall mounts, but you can build a good system around their product.
Another ID company u could look at for small bookshelves geared toward the high end is Philharmonic Audio, Affordable Accuracy +. He also offers a Center that is budget friendly.
Also, Ascend Acoustics has their CBM170s on sale right now. I've heard good things about them for small speakers.
Just some ideas to maybe help out.
Happy Hunting!