Here's a estimate quote from NADA guide's web site:
Boats and Personal Watercraft
Model Name/Description: PARTY BARGE 25 REGENCY(*)
Boat Type: Pontoon Boats
Hull Material: Aluminum
Beam: 8' 6"
Net Weight: 2220
(Low Retail) $5,770 (Average Retail) $6,540
Power Boat: MISCELLANEOUS OPTIONAL EQUIPMENT
Hardtop 21' - 25' Boat $1,505 $1,710
TOTAL PRICE (Low Retail) $7,275 (Average Retail) $8,250
Suggested List: $14,895 (Original MSRP when new)
You can get a rough resale value estimate on almost all boat manufacturer models at www.nadaguides.com
A word of caution. If you plan to ONLY use the boat as a swim platform and for crusing around, it should do that well.
However, if you intend on needing a boat to do any of the following watersports: (skiing or wakeboarding), a pontoon boat will simply NOT work, especially this model you are seeking to buy is extremely underpowered for that purpose.
Pontoon boats perform horribly when it comes to towable watersports. A good compromise is a deck boat, a regular hulled boat that is slightly larger in size than a regular ski boat of the same length. It also has more passenger capacity than a regular ski boat as well, but about slightly less passenger capacity than a pontoon boat of the same length. Most deck boats also have a reasonably powerful drive system that provides enough HP to get around and tow people on the water well.
At only age 28, I've accumulated a lot of experience regarding what expectations and needs are required for individuals/groups/families when going boating.
Usually what happens is an individual or a family buys a pontoon boat thinking that using it as a swim platform and crusing around is enough. Not enough careful thought and planning goes into the "what I really expect of the boat to do now and in the future."
So, when the kids grow up or you as the parents want to do some fast watersports, you gotta buy a different boat now or buy a powerful 3 seater PWC to go with the pontoon boat.