If you do want to go but worry about the financial impact then often it is best to book your holiday in advance. You can usually book 18 months or so in advance, giving you plenty of time to split the cost down and pay for the holiday monthly. Most tour operators will ask for a small deposit, often even as little as £50 per person and then allow you to pay for the holiday in monthly parts as long as the balance is paid in full at least 6 weeks prior to travelling.
If you would rather book a last-minute deal that often offers you great value for money then you should consider taking out a 0% credit card. Not only will this allow you to spread the cost out but it can also give you that bit of added protection by paying on a card.