Everyone doesn't have basic income added to their income, unless the government is printing money to pay the basic income. Basic income redistributes funds from one or both of two other sources: 1. Existing social benefit programs benefits + administrative costs, and/or 2. Taxes, (in most proposals where additional tax revenue is seen as part of the funding stream, this is a progressive tax on total income).

That being said, the redistribution should result in more money chasing certain goods and services, which should increase the price for those. With realistic elasticity levels, the increase in price will be less, proportionally, than the increase in the quantity of money available for the goods/services, and the market clearing quantity of those goods/services produced and sold will increase.

It will also result in less money chasing other goods and services (public sector administration for the "replace conditional benefits program" part, and goods that are disportionately attractive to wealthier purchasers for the "funds from progressive income tax" part.)