We did Cirque du CarnEVIL last year on a fairly tight budget (there's a huge thread with loads of ideas amassing 140 pages but u can also find some stuff in my albums)
Here's some of what we did...
1)Banners and Concession signs...old sheets (if u don't have any to sacrifice call hotels and grab some for free) and paint...cheap and easy.
2)Cotton Candy...Polyfil (about $3) soaked in a solution of paint and water...let dry and affix to cones made out of rolled up paper or put in bags. I also added cockroaches to mine. I made a display box to show them off in.
3)Clowns...search Goodwill, often you can find costumes dirt cheap and if your lucky enough to find a mask just repaint it...just about any mask can be repainted to look like a clown.
4)Marque sign, for about $10 worth of materials it's a show stopper. Poster board, foam board, spray paint and lights
5)Games:
Dead Ringer...I did a large display with DT body parts elevated on dowels...and now is the perfect time to find clearance pool rings.
Tempt Your Fate..balloons and darts
Eye on the Prize (or u could call it U sink it U drink it and turn it into a drinking game)...I grabbed the nicer plastic cups from DT about 5 pks of 10...grab some red paint and drip blood around the rim of about 10 cups...glue them down on a board so they are all touching each other in a grid formation (the bloody ones randomly spaced)...then grab ping pong balls also from DT (I panted mine to look like eyeballs)... Only the bloody cups are winners
Games we ran out of room for:
Grab 6 DT skulls and stack them in a pyramid...use DT squishy balls to knock them down
Instead of duckies you could do a pool of bloody water with DT ears (just paint the number on the back)
Buckets...cheap wooden buckets or laundry baskets placed on an angle and some overinflated balls
6)Walls
DT tablecloths...we covered our garage walls in alternating colors to look festive
DT balloons (14 ct jumbos) I grabbed 2 packs and as I was not paying for helium I simply pinned them to the walls in large clusters. Then I spread spider webbing over them and placed huge hairy spiders that I already owned on them and the walls
7)Music
Nox Arcana, Carnival of Lost Soulf
The lighting is your biggest thing...tons of lighting be it Christmas or just colored lights.
Food: we did popcorn,cotton candy, funnel cakes, corn dogs, snow cones and lemonade...don't take that much on it bout killed us... Funnel cakes and corn dogs r a must...my 3rd fave would be cotton candy cause it was fun...but everyone loved the popcorn (we rented our machines for $35 each...this was my big splurge)
We did an oddities room...I worked for hours and the room was hardly even noticed
Don't set your heart on an outside party, I did...and we were rained out

Though everything looked awesome inside I wasted a ton of time on props I couldn't display..,