I designed a touch PCB keypad what can I do for silking and covering
Let's assume that the box is fully waterproof, I would still recommend using a box as  the one Michel suggested. The main reason for this is the transparant cover. You really don't want to drill holes in the cover and try to make everything water proof so what is easier then mounting everything inside. With the transparant cover you can easily read the lcd and you can mount capacitive buttons on the inside of the lid. Example in figure below. *image taken from Source image



regarding the touch buttons themselves, the capacitive touch buttons are quite easy to do, they are being used extensively for this purpose. I would suggest reading the "TI slaa576a" Design Document Design Document the document describes the theory of operation and the ways you can design your buttons, which materials you can use and so on. As far as IC's go there are lots of options to choose from, fully assembled breakout board based on the "Atmel AT42QT1070" or the "microchip MTCH101" or a lot more options.
Pricing and cost will be determined by your final solution but should definitely not break the bank. The IC's I listed are both available for less then 1 euro.