I have made many things for my home rather inexpensively since I prefer unique things to things prefabbed and mass produced.
For a coffee table get a piece of wood the size you want the table to be...and sand the edges to make them rounded if you don't have a router. Buy the cheapest you can find since it doesn't really matter. Then finish only the top...either paint or use a wipe on poly. This whole thing should be able to be made for under $12...then add the legs...for this I have used(for toddler beds, school tables, other tables) plumbing pipes. Use the cheap galvanized pipes...get 4 flanges that you attach to the underside of the wood with screws then get "legs" the length you preferand screw those into the flanges. You can also get caps for those as well. This can be pricey if you dont' go with the cheapy pipes...remember they aren't holding anything in them. Another option is to use the PVC pipes...I haven't tried it, but I am sure it would work and then you could paint them to coordinate. This is a really cute and simple look...very clean lines.
For curtains, the easiest thing I have done is purchased cheap plain white sheets...they are already hemmed for you and since you aren't sleeping on them, they just need to look nice rather than feel nice. Plain white or ivory muslin works very well also and is VERY inexpensive. For my living room, I put grommets all along the top of the sheet, and then tied pretty white roping in loops...cheap and looks VERY cool...like a sleek tab top curtain. Then for the rod I took a long dowel(it is a 10 foot window) and ended with 2 cheap finials and spray painted the whole thing black. I also painted the little holders that hold up the dowl black...the holders and finials I bought unfinished at Lowe's for about $2 each. The curtains very easily slide back and forth along the rod for privacy. It was the easiest and cheapest window treatment in the house...I think, if memory serves, I only ended up spending about $40 on the entire thing.
Slip covers are easy to make, with many directions on the net for tthem. I also bought some at Target very inexpensively.
Knickknacks I buy as I find them rather than going on a hunt for them. I find things on sale, etc. For example we just redid the 1/2 bath on the first floor and I needed some quite things for the walls. I kept my eye out while doing my normal day to day stuff and found 4 pictures and a wall planter and fake plant for the bathroom along with hand towels and spent only $10 on the entire thing. If I had gone out looking for them I could have easily found things just as nice and spent more for them, but exercise patients and the things will find you. A good source of nice things around the house are kid related. Rather than just hanging sheets of paper the kids have doen on the wall...buy cheap frames from Walmart---usually can get them under $2 a piece and have the kids make things specifically for the room...it will look more purposeful and less cluttered.
Table cloths...I buy them ONLY at Pier One...and only on sale. My mom and I went there about 2 weeks ago and she got 8 placemats, 8 napkins and 1 table cloth for $25 total including tax. They were basic neutral ivory too....so that was a good deal for something that would work in EVERY house. Pier one also puts a lot of their knickknacks on sale and I just go through there and through crate and barrel for the sale stuff.(I spent $13 the other day at Crate and Barrel on stuff for my newly retro painted kitchen and came home with a rug, dish towels, a vase and a pitcher)
Rugs can be expensive. I bought my last oriental from a dry cleaner...called around since they will only hold things for 30 days and usually sell things CHEAP after that to get it out of the building. I have a nice oriental rug I bought for $35. I spent about 3 days calling around to places in the area, but it worked

. Also, I have seen inexpensive ones at walmart, homedepot and lowes as well as at bed bath and beyond and linens and things.
For the chair...that may be hard to get under $200 with all the other stuff...could you get away with getting a wooden chair just to have extra seating rather than getting an upholstered one? Put a nice cushy pillow on it and it should be fine. I used for years 2 of those upholstered dining room chairs I got from a neighbor as the chairs in my livingroom. They are not soft and cushy, but do the job of providing extra seating quite well. Another option is to make or buy and ottoman...provides extra seating as needed as well as a foot rest after a long day chasing kids
Hopefully this isn't too much information or too much useless info...

This is my love...decorating on a budget and I enjoy doing it. Have fun! Look at it as an adventure rather than something you have to get over with in one shopping trip. It will look more like "you" this way.