Ok, got it!
Here is the summary of the changes:
1. The Plugins\SevenSpikes.Nop.AjaxFilters\Views\PriceRangeFilterSlider7Spikes\PriceRangeFilterSlider.cshtml now reads like:
@** Copyright 2012 Seven Spikes Ltd. All rights reserved. (http://www.nop-templates.com)
* http://www.nop-templates.com/t/licensinginfo
*@
@using Nop.Core.Infrastructure;
@using Nop.Services.Catalog;
@{
    Html.AddScriptParts("~/Plugins/SevenSpikes.Nop.AjaxFilters/Scripts/PriceRangeFilterSlider.min.js");
    var priceFormatter = EngineContext.Current.Resolve<IPriceFormatter>();
}
@model SevenSpikes.Nop.AjaxFilters.Models.PriceRangeFilterSlider.PriceRangeFilterModel7Spikes
<div class="priceRangeFilterPanel7Spikes" data-currentCurrencySymbol="@Model.CurrencySymbol">
    <div class="block filter-block">
        <div class="title">
            <a class="toggleControl">@T("SevenSpikes.NopAjaxFilters.Client.PriceRangeFilter.Title")</a>
            <a class="clearPriceRangeFilter">@T("SevenSpikes.NopAjaxFilters.Client.Common.Clear")</a>
            <div class="clear"></div>
        </div>
        <div class="filtersGroupPanel">
            <div class="priceRangeMinMaxPanel">
                <span class="priceRangeMinPanel">
                    <span>@T("SevenSpikes.NopAjaxFilters.Client.PriceRangeFilter.Min"):</span>
                    <span class="priceRangeMinPrice">@priceFormatter.FormatPrice(Model.MinPrice)</span>
                </span>
                <span class="priceRangeMaxPanel">
                    <span>@T("SevenSpikes.NopAjaxFilters.Client.PriceRangeFilter.Max"):</span>
                    <span class="priceRangeMaxPrice">@priceFormatter.FormatPrice(Model.MaxPrice)</span>
                </span>
            </div>
            <div id="slider" data-sliderMinValue="@Model.MinPrice" data-sliderMaxValue="@Model.MaxPrice"
                data-selectedFromValue="@Model.SelectedPriceRange.From" data-selectedToValue="@Model.SelectedPriceRange.To" >
            </div>
            <div class="priceRangeCurrentPricesPanel">
                <span class="currentMinPrice">@priceFormatter.FormatPrice((decimal)Model.SelectedPriceRange.From)</span>
                <span class="currentMaxPrice">@priceFormatter.FormatPrice((decimal)Model.SelectedPriceRange.To)</span>
            </div>
            <div class="clear"></div>
        </div>
    </div>
</div>
2. In the Plugins\SevenSpikes.Nop.AjaxFilters\Themes\NeoFashion\Content\SevenSpikesNopUI.css
I've changed (or added) the following styles:
.priceRangeMinMaxPanel {
    overflow: hidden;
    margin-bottom: 10px;
    text-transform:none;
}
.priceRangeMinPanel .priceRangeMinPrice {
    text-transform: lowercase;
}
.priceRangeMaxPanel .priceRangeMaxPrice{
    text-transform: lowercase;
}
.priceRangeCurrentPricesPanel .currentMinPrice {
    float: left;
    text-transform: lowercase;
}
.priceRangeCurrentPricesPanel .currentMaxPrice {
    float: right;
    text-transform: lowercase;
}3. In the Plugins\SevenSpikes.Nop.AjaxFilters\Scripts\PriceRangeFilterSlider.min.js
I've replaced all occurrences of:
x + z.toFixed()
into
z.toFixed() + ' ' + x
where x stands for $(".priceRangeFilterPanel7Spikes").attr("data-currentCurrencySymbol")
and z stands for specific values
Now everthing works and looks correct.
Thank you.