What current the part can carry, how much electric flow can go through it without burning it up is big part of the cost. The flow of electric current causes heat.
A resistor or SSR with small capacity costs less than one with more capacity. So you can't find just the name of a part and consider the price of that one typical of all with the same name.
SSR's are solid state and may switch fast with no ill effect. A low capacity SSR will be much cheaper than a heavy duty SSR but -all- SSR's are the solid state with ability to switch fast up to the limit of each.
When I tell of a resistor rated in watts that is the most electric it can take in terms of voltage times current which is watts which equals power.
Power in watts is voltage x current.
Voltage is the push, the electrical pressure that moves current (flow of electrons). This is a bit simplified but for what you do, it applies.
Current moving in that pressure makes the heat. Parts that can take more heat are "bigger" and cost more.
Ohm's Law (where law is what is always observed in the real world) is the relation of voltage, current and resistance.
You start with voltage and current, resistance comes in (only superconductor has none) and making heat becomes more understandable.
But for now you need to see that parts that have more capacity for current flow cost more. You don't have to calculate that.
I have cheap relays to switch up to 10 Amps of house power (here 120VAC) able to run many things. Tiny power from Arduino can turn the relay ON and OFF, and I am careful to not make it do that too frequently for long. For about $2 I have a switch that can flow a good deal of power. An SSR with equal capacity typically costs much more but sometimes a discount can be found (so can a fake, some deals are steals and some steal you) and for me, I got the relays since I don't need to turn ON/OFF even 1 time per second.
What is practical depends on what you require done.
You also need total circuit given, you are not ready to design.
If SSR is a must have then your circuit needs one with capacity to do the job and every other part to do its job, you are not ready to find those out so you get help here and from your relative who knows. I am limited in my hardware knowhow, others here will help you better, I just try and keep you from the worst and tell you there is hope.
With an Arduino, some wire, a low-rated resistor and capacitor and a bit of foil a sensor can be made that detects a finger close or touching. It can sense through wood or plastic and be used as a button with no moving parts. It has a very long lifetime.
But think that this thing uses an invisible electrical field that meshes with your own invisible electrical field to detect your finger, it is a touch button even if it's a bit crude and it demonstrates the truth of electric fields in and around us all. Wonder about that!