First things first, there is potentially exposure to two different taxes here.
The person disposing of the land may realise a gain that is subject to CGT (Capital Gains Tax).
The person(s) acquiring the land may be in receipt of a gift that is subject to CAT (Capital Acquisitions Tax).
CGT:
The amount of money that changes hands is irrelevant in a transaction like this, all that matters is the market value - their gain is calculated as the difference between the cost of the land when they acquired it (or its value when they acquired it if it was willed/gifted to them) and its value when they disposed of it.
There is a relief, and it is outlined at Page 16 of the CGT1 guide to CGT, and also in Revenue's manual - as a previous poster mentioned it only applies to a transfer to a child (not a child and their spouse), but can be worked around as you'll see from the underlined bit at the end:
[19.7.2A] Transfer of site to child (S.603A)
2A.1
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]This section provides that capital gains tax will not apply on the transfer of a site from a parent to a child (as defined) where the transfer is to enable the child to construct his/her principal private residence on the site. [/FONT][/FONT]
2A.2
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]The value of the site must not exceed €500,000 (€254,000 for disposals prior to 4 December 2007) to qualify for the relief. For disposals on or after 1 February 2007 the site cannot exceed an area of 0.4047 hectare (1 acre) in addition to the area occupied by the dwelling house itself. [/FONT][/FONT]
20.3 [FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]If the child subsequently disposes of the site without having occupied a principal private residence on the site for at least three years, then the capital gain which would have accrued to the parent on the initial transfer will accrue on the child and a clawback of relief will arise. However, this gain will not accrue to the child where he or she transfers an interest in the site to his or her spouse. [/FONT][/FONT]
CAT / "Gift Tax":
There is a lifetime threshold for the value of gifts that you can receive from a parent tax free - if the amount paid for the site is below the market value then the difference is a gift from parent to child, which eats into this threshold.