I would not buy plastic tips just to save money. Instead I would buy just the metal tips that you need instead of wasting money on tips you will never use. I bought a set when I first started out decorating and most of the tips I don't use. You will get much longer life out of metal tips compared to plastic so you will save money in the long run. Just my humble opinion.
If you are asking for inexpensive tips because you need them for a group or kids: you can also snip the ends of parchment bags: make a V for leaves, 3 tiny Vs for stars, and diagonals for roses. Straight cuts in differing sizes make #1-12, of course.
That's how I started out! Wouldn't recommend it, but if you are in a pinch...or on the road... 
never know when we have to decorate!
Oh my gosh no, I am not trying to buy them for me to use I am buying them for mothers day to give to children to decorate the cake for their moms. That is why I wanted to go plastic so I could just incorporate them into the price yet still keep the prices low. Thanks for trying to save me though. lol You are still my heros
Have you tried your local grocery store? Here in Canada (where I live anyway) they have a few in a package that you could get in the cake/bake goods isle).
I also have seen them in Michaels as well (can't recall how much $$) and you could use their coupons. or you could try
Amazon.com
They have the Betty Crocker 100 Piece Cake Decorating Kit for ($8.99)
or you can get the 9 Ekco Cake Decorating Kit for $2.99 which comes with:
* Pullout plunger pushes filling smoothly through decorator's cylinder
* Convenient thumb lever and ergonomic design provides comfortable grip
* 8 different tips included; dishwasher safe for quick, simple cleanup
Depending on how many you need you can always use the free shipping feature as well.
Hope that helps! 
I was just on Wilton's website and they do carry a small Tip and Nail Set (5 tips and a nail for $1.99). I believe that Hobby Lobby has 40% off all Wilton products (no limit) but you'll need to print off the coupon from there website first. So if they have it there for the same price you could pick up the kit for $1.19. I think the sale is on until the 12th. I you get this on time!
Parm
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