Learn English – Do I need a comma before “perhaps” in the following case

Either is ok. Commas indicate a pause. If you want to emphasize the contrast between the two clauses more, add the comma.

By the way you don't need the "to me" in that sentence; it's implied by the fact that the sentence is written in the first person ("I" is the subject).

I like your car, but it seems too expensive for you.

Advice from the BBC:

A comma (,) generally indicates pauses in speech. But, when it joins two clauses, it indicates a contrast between two ideas. In speech it is normal to draw attention to this contrast by a slight pause. A comma is the usual way of indicating this, although it is not obligatory:

Sheila can eat anything and large quantities of it, but she never puts on weight.

I'm going to make some New Year resolutions, but I don't suppose I'll keep them

The comma can represent a syntactic pause and/or a change of intonation that accompanies and corroborates a syntactic pause.

A comma would make clear that "then" as used here is not temporal but conditional; temporal and conditional uses of then have different syntactic pauses and intonational contours.

P.S. Its being at the end of the sentence is not the deciding factor. Consider:

**I'm away Monday, but I'll be in town on Tuesday. Can I see the apartment then? [no pause before "thenn"]

The answer on the rental form is incorrect. I have no pets. I can rent the apartment, then?** [pause and different intonation to mark the meaning "in that case"]