Take a look at this chart:

In July 2010, George Osborne stated that the full £20bn cost of renewing the UK's Trident nuclear deterrent must be paid for by the Ministry of Defence.
Adding further, Mr Osborne said he had made it "absolutely clear" the Trident costs were part of the defence budget, "All budgets have pressure. I don't think there's anything particularly unique about the Ministry of Defence".

"I have made it very clear that Trident renewal costs must be taken as part of the defence budget," he said.

At the time, the then Defence Secretary Dr Liam Fox, warned it would be "very difficult" to maintain other MoD projects if more than half its budget went on funding Trident. He warned against complacency as he defended the renewal of Trident as the most "cost-effective way of maintaining Britain's nuclear deterrent".

"Should Iran become a new nuclear weapon state, Saudi Arabia, Egypt and Turkey would be likely to follow suit and we could see ourselves in a new nuclear arms race," he said.

"There are a lot of real dangers out there and I'm not sure people have really focused on them."
He told the paper reducing the Trident fleet to three submarines would put extreme pressure on the UK's policy of keeping one nuclear missile-armed craft at sea at all times.

Nearly two years down the line, it would seem Dr Fox could be somewhat vindicated in his statement, however, looking at the chart (above) the £20 billion figure suggested for Trident renewal appears a little low if Nick Clegg's comment in April 2010 is to be taken seriously. He suggested at the time that renewal of Trident would be closer to £100 billion.

Under the UKIP Defence Policy, they propose to "Maintain Britain’s independent nuclear deterrent with existing Trident submarines and then replace them with four British-built submarines armed with US missiles"

It'll be pretty costly to do that.
Four submarines would likely be insufficient too, considering to keep just one at sea, three must be kept in reserve!

The MoD are simply bankrupt. They can not possibly cover the bill for the renewal of Trident.

Ultimately, UKIP should bin Trident. It would be far, far cheaper to hire up-to-date modern submarines off the United States, train and crew with UK servicemen (within 48 months).

The money saved would certainly allow the MoD to re-establish a credible ground force, manage a land based deterrent, secure aircraft procurement for the new aircraft carriers within a tangible time frame, and bring back training centres which have been closed down / decommissioned under this Governments reign.
Keeping in mind Scotland's agenda to become 'autonomous' is not going to go away, expansion of the southern Naval port therefore would be advantageous, at the very least, prudent.

Further, the bi-lateral agreement with France should be immediately scrapped. No more money should be poured into projects which ultimately do not serve UK interests; in basic terms, good 100% communications "in battle" is the difference between winning and loosing.
A joint military-alliance between the USA and UK means everybody is singing from the same hymn sheet; NATO campaigns or military operations are blighted by poor communications due to multi-linguists, different calibre weapons and vehicles, etc.

Presently, the UK can not afford to maintain its 'world player' status. To the point, we're broke, and can not even maintain a credible home defence, which is utterly shameful.
Priorities / common sense needs to be applied 'at home', which means of course cutting away the 'fat from the meat', but not down to the bone, the latter, an exercise which this present Government appears to be hell-bent on completing.

When the UK is in a position to fully defend home and sovereign waters and interests, maybe then it will be time to move back up a gear, and take a leading position on the world's stage. The UK can not lose sight of the fact that unlike the last century, the nature of modern warfare has considerably changed.

Scrap Trident, time to adapt.

Further reading

UKIP Defence Policy