All kinds of cheap push daggers out there for less than $30. Just let your fingers do the walking.
I've got a couple that I bought (one's a Cold Steel Urban Pal) but never carry them. I prefer to carry a folder and/or a Marcaida Pika kraambit instead. But, if you'd like a suggestion, check out the MT2046BK double dagger set made by M-Tech that you can buy for less than $20.