You need multi-band antenna to operate on cellular network. This is difficult antenna to implement. First of all it has to be tuned to multiple bands specified in your module you plan to use on the network you will be working with (low bands in range 824 to 950 MHz, high bands - 1800 MHz to 2100 MHz - subset of that) next you have to pass approvals to be able to operate on your network and in particular demonstrate that your system (module and antenna) radiate more then minimum required TRP (total radiated power) and receive with minimum required TRS (total received sensitivity). To be able to pass the tests you must have properly designed and tuned antenna and overall size of device (antenna and groundplane and combination of all conductive bodies in your device) - is critical. The certifying body in North America: PTCRB. Over the years I designed multiple antennas for cellular modules for different networks successfully - my antennas usually pass PTCRB pr-screening tests from the first time (if I am allowed to do things my way). However this design does not happen overnight. Let's say if you ask me to do this antenna for you and allow me to pick the overall device size (will be like medium size iPhone) and let me pick how much space antenna element will take on PCB (~ 2 inch square) - this will be relatively easy case for me and it will take me ~ 1 month. If your device is overall small or you do not have sufficient space on PCB for antenna element or have some special features - complexity of design increases and time increases. Consequently it will be expensive.
Not sure this is the answer you expected, sorry.