Oricât de mare este taxa de participare, o plătim.

Oricât de is a common Romanian pattern meaning however or no matter how before an adjective or adverb.

So:

• oricât de mare = however big/high
• in this sentence, with a fee, it is naturally understood as however high

It introduces a concessive idea: the main action still happens regardless of the size of the fee.

When oricât is followed by an adjective, Romanian normally uses de:

• oricât de mare
• oricât de greu
• oricât de scump

So de is just part of the standard structure here. You should learn oricât de + adjective as a set pattern.

Mare agrees with taxa because it describes the fee.

A useful detail is that mare has the same singular form for both masculine and feminine:

• masculine singular: mare
• feminine singular: mare
• plural: mari

Since taxa is singular, the correct form is mare.

Because taxa means the fee, while taxă means a fee.

Romanian usually puts the definite article at the end of the noun:

• taxă = a fee
• taxa = the fee

So taxa de participare means the participation fee.

De participare specifies what kind of fee it is.

• taxa = the fee
• taxa de participare = the participation fee / fee for participating

Romanian very often uses de + noun to make this kind of noun phrase.

Este is the 3rd person singular form of a fi (to be), and it matches taxa, which is singular.

So:

• taxa este mare = the fee is high

In everyday speech, many Romanians would also say e instead of este:

• Oricât de mare e taxa de participare, o plătim.

Both are correct; este is just a bit fuller or more formal.

The first part, Oricât de mare este taxa de participare, is a subordinate clause. The second part, o plătim, is the main clause.

Romanian normally separates this kind of introductory concessive clause with a comma.

So the comma marks the division between:

• however high the participation fee is
• we pay it

O is a direct object pronoun meaning it here.

It refers back to taxa, which is feminine singular, so Romanian uses o:

• taxa = feminine singular
• o = it for a feminine singular direct object

So o plătim literally means we pay it.

In Romanian, short direct object pronouns usually come before a finite verb:

• o plătim = we pay it
• îl văd = I see him/it
• le cunosc = I know them

So o plătim is the normal word order.

Romanian often leaves subject pronouns out because the verb ending already shows the person.

Here, plătim means we pay:

• plătesc = I pay
• plătești = you pay
• plătește = he/she pays
• plătim = we pay

So noi (we) is not necessary, though you could add it for emphasis:

• ... noi o plătim.

Not in this sentence.

With a normal finite verb in an affirmative clause, Romanian uses the clitic pronoun before the verb:

• correct: o plătim

You may see pronouns attached after the verb in other situations, especially with imperatives:

• Plătește-o! = Pay it!

But here, o plătim is the standard form.

Yes. That version is also natural.

There is a slight nuance:

• Oricât de mare este... = more direct, more factual
• Oricât de mare ar fi... = more hypothetical, closer to however high it may be

Both are good Romanian. The version with ar fi sounds a bit more abstract or concessive.

Literally, mare often means big, but with prices, costs, fees, and amounts, English usually translates it as high.

So:

• o taxă mare = a high fee
• not usually a big fee in natural English

This is a normal meaning extension in Romanian.