Return Last Valid Record When Query Is Outside The Range?

Using MSSQL 2008 R2

Given the following table

Code:
{ID, PropClass, OffSet, Amount}
{1, 1, 1, .30}
{2, 1, 2, .45}
{3, 1, 3, .50}
{4, 2, 1, .26}
{5, 2, 2, .15}

If I know the exact offset I can query easily enough using PropClass and the exact offset. But what if the offset is not included in the range for a given PropClass? How can I get a query to return the last valid record for a given PropClass from within a join?

For example, if my query contained PropClass = 1 and offset = 4, it should return the Amount of .50 from Record with ID 3

This is a query that I am trying to work on:

Code:
SELECT v.District, v.PropClass, YearAquired, SUM(cost * cnt), SUM(v.Cost * v.Cnt * t.Amount), SUM(v.Tax), COUNT(*)
FROM UPValue v
INNER JOIN UPMaster m on m.Year = v.year and m.Account = v.account
INNER JOIN UPTable T on t.PropClass = v.PropClass and t.Offset = v.Year - v.YearAquired
WHERE v.Year = 2012 and LeaseType = 2
group by v.District, v.PropClass, YearAquired
order by v.District, v.PropClass

Using <= will not work because that would return multiple records from UPTable when the offset is < the max offset.