Further to Chris�s answer, the starting point for a fine in the magistrates� court for a first time offender pleading not guilty to this offence is a fine of half a week�s �relevant weekly income�. (This is essentially net income after deductions). For those unemployed or otherwise in receipt of little income, the lowest figure used is �100 pw. This means a fine of �50 would be levied.
A guilty plea would reduce this to �33 (in practice, the bench would probably round this up to �35). However, you would also be liable to pay prosecution costs (around �45) and a �15 Victim Surcharge (VS), making a total of around �95.
The Bench does have discretion to waive the costs (but not the Victim Surcharge). An example of this is where people have been unable to accept a fixed penalty (FP) because, say, their driving licence is with the DVLA for amendment. In this case they have to go to court, but because they would otherwise have accepted the FP the magistrates may award a fine of �45, �15 VS bringing the total to the FP equivalent.
They would be unlikely to do this in your case. You would have chosen to go to court simply to ask for time to pay as this facility is not available via the FP system. They would probably take the view that if you can afford to run a car and a mobile phone, you ought to be able to raise �60 within a month.