What are the standard cables I can use for modbus protocol? lease add the price details if anybody knows
There are no universally standard cables per se, but the most popular implementation of Modbus is Modbus RTU, which will work over any 8-bit asynchronous serial line, like EIA-485. Unfortunately, EIA-485 doesn't specify any sort of standard cable or connector either, beyond that it be a shielded twisted pair. Modbus doesn't even specify a shielding requirement.
So, what you use is not really dictated by anything beyond cost and availability. For Modbus, OR EIA-485, it is pretty hard to beat good old registered jacks and Cat5 twisted pair cabling. You are already likely familiar with these cables and connectors, as they are used widely for Ethernet. Your computer or router is almost certainly using it right now. Economies of scale have made the price and availability of these jacks and cables very attractive, so a lot of things besides ethernet use it.
Now, ethernet even at the lowest end is much faster than ModBus. For Modbus, you can use Cat5 cable. This is probably the cheapest twisted pair cabling you'll find, as it is unshielded. If you need shielding, you can upgrade to Cat5e.
Another option of course is simply sending ModBus over actual ethernet. There is a version of ModBus that operates on top of an Ethernet networking layer as TCP frames. This of course requires a full TCP/IP stack and ethernet magnetics and what not on either end, so this is not going to be a cheap option....unless you happen to already have networking in your application. In which case, it is effectively free, as you can just piggy-back it on something you already have.
So, in short, you can send ModBus over any twisted pair cable. There is no agreed upon standard cable or connector in use, nor is there a need. ModBus is a master-slave protocol, and so by nature is going to be very application specific. There is little need for interoperability, so just use whatever is robust enough for the speed and distance in your application.
As for prices, the fancy stuff (shielded, cat5e), can be had complete with connectors on the ends for almost nothing. There is probably even cheaper out there, but a quick google lead me to this 3 foot Cat5e cable, which costs a princely sum of 74 cents. Yep, $0.74. If you don't mind crimping connectors on the end yourself, you can get any length you want for 19 cents a foot here. But again, shop around. If you buy in bulk 1000 feet spools, you can get cat5 cabling for as little as 3-4 cents per foot.