As you can use an action to, dash, dodge, attack, cast spell, etc.
Am I allowed to walk my normal movement >> use my action to dash >> then use 2 SP to quicken a spell/cantrip?
My DM reasons like this:
Because I chose to Dash with my action, I do not have any action available to convert into a bonus action and I cannot do what I described above. The official ruling says: "When you cast a spell that has a casting time of 1 action, you can spend 2 sorcery points to change the casting time to 1 bonus action"
I would plead that making that spell a bonus action would not require me to have an action available. And is counted as a free action.
Best Answer
Metamagic has no action cost, order is entirely up to you
There is no action cost listed (only the resource cost) for utilizing any Metamagic abilities, so your action remains completely available.
In your specific case, the options are as follows:
Use your movement
Use your action (dash)
Spend Metamagic resource to convert Spell to a Bonus action
Use Bonus Action
Timing of Movement and Actions are also up to you:
In addition Bonus Action timing is stated as:
Breaking up Movement for Actions and Bonus Actions
You can break up your movement however you like on your turn. For more details, see this related question on how characters can move and act during their turn and the answers there.