Tires are increasingly expensive ... This is always a possibility given the myriad sizes that each model is available in. When you’re ready to buy, try negotiating the price from your local ...
There are multiple components like the chain, swingarm, brake lines, etc, that a bigger tyre could foul with. It is always better to stick to the sizes the bike originally came with.
Road bikes are pretty awesome — designed with lightweight frames, narrow tires, and aerodynamic features ... most bike manufacturers will have a sizing chart available with recommendations on bike ...