cost

You won't have a whole lot of fun in Belize with that budget- less than $50 a day. Sure you can rough it but in your late 50's do you want to?....you'll get meals, beers and a bed (just about) but if you are going to travel that far then have more spendies and enjoy!

Agree that is a pretty tight budget for Belize..esp. if you want to do lots of activities (caves,diving etc.)

If you just want to eat,drink and sleep...you can do it ;-)

Cheapest place to fly to from the UK will be Cancun in Mexico..then take a bus into Belize.

Accommodation
On a low budget, you can find dorm beds for about BZ$20 a night. Private room with shared bathroom is around BZ$30. Private room with bathroom start at about BZ$40.
This site has a selection of lower budget hotels...
http://www.belizeexplorer.com/

Food
You can survive on about BZ$20 per day (that's eating rice & beans, a lot of bananas and no alcohol), but BZ$30 might be a better amount to use in your budget. Beer is about BZ$2.50 if bought in a shop -- double that if bought in a bar.

Travel
Buses are cheap. For example: Corozal to Belize City is BZ$9; BC to San Ignacio is BZ$7. Work on 10 to 15 cents per mile.

Water taxis (ferry boats) go to the cayes -- the water taxi services have websites with schedules & fares.

The BelizeBus site has a lot of transportation information.

If you fly to Cancun, you can get a bus as far as Chetemal then boat to San Pedro or Caye Caulker sanpedrowatertaxi.com/

Here are a couple of good low-cost, popular options, for example:
[The Trek Stop|] west of San Ignacio
[Yumas Hostel|] on Caulker Caulker

If you keep your food simple or stay in places like that where you can do some/most of your own cooking, you can keep costs down. What would really bust my budget - more than lodging or food - would be tours. Belize has some really outstanding ones, but they'll blow past your daily budget and I'm not sure you'll be able to save enough in other ways to afford them. For example:
ATM cave
Actun Chapat
Raggamuffin snorkeling/sailing trip

Hey fellas, i realy thank you for your straight sound advice, as from now i'm realy looking into it all, and i will try to double my cash, i'm thinking that after going all that way there's no point in not actually seeing places, and doing thing's (trips ect) i'm sure i will be in touch for more info before i depart

Always sound advice - take half the stuff and twice the money. ;-) I've pasted my favorite Belize links below - have a great trip!
______________________

My photo collections with blog, travelogue, and review links: http://www.flickr.com/photos/staceyholeman/collections/

My travel blog starting in 2012 (earlier ones linked with the photo collections):
http://hopefulistinlatinamerica.blogspot.com/

My descriptions and reviews on Trip Advisor:
http://www.tripadvisor.com/members-reviews/hopefulist

Guidebooks I like: Moon Handbook, Fodor’s Guide, and Explorer’s Guide.

Laminated wildlife identification cards: http://rainforestpublications.com/belizeFieldGuides/index.html

A very cool checklist book for Belize for the young or young-at-heart: http://www.amazon.com/Play-Belize-Mesa-Somer/dp/0615198546/ref=sr_1_2?ie=UTF8&qid=1330549187&sr=8-2
- - -
Budget to midrange lodging site: http://www.belizeexplorer.com
Great island and lodging downloads: http://www.belizefirst.com
Informative transportation blog: http://www.belizebus.wordpress.com
- - -
Shuttle recommendation: http://www.parrot-nest.com/belize-shuttle.html
Zoo: http://www.belizezoo.org
Great jungle camp in Cayo: http://www.belizecamp.com
Great budget lodging in Cayo: http://www.thetrekstop.com
Great value hotel with pool in Cayo: http://www.aguadahotel.com
Don't miss cave trip: http://pacztours.net/actun-tunichil-muknal/
Another, less-visited amazing cave option in Cayo: http://www.actunchapatadventure.blogspot.com/
Lodge with lots of adventures: http://www.cavesbranch.com
- - -
Roxy Ortiz - fabulous, fun tour guide: http://www.tikalroxy.blogspot.com
My favorite hotel at Tikal: http://www.tikalinnsunrise.com
Good choice in El Remate, Guatemala: http://www.30minutesfromtikal.com/
Favorite midrange places in Flores: http://www.corpetur.com
Good value budget option in Flores: La Mesa de los Mayas, mesamayas@hotmail.com
- - -
Great inn in coastal Garifuna town: http://www.hopkinsinn.com
Garifuna drumming center: http://www.lebeha.com
- - -
Apartment on the beach on Caye Caulker: http://www.staycayecaulker.com/sailwinds.html
Another Caye Caulker option: http://www.gocayecaulker.com/accommodations/maxhapan-cabanas
Great day snorkeling trip: http://raggamuffintours.com/hol-chan-snorkel/
- - -
Very rustic atoll experience, cheap if you have a week: http://www.glovers.com.bz/
- - -
A few more for good measure (2012 trip):

Great jungly place near Punta Gorda: http://www.hickatee.com
Off the beaten track diving and snorkeling, Sapodilla Cayes: http://www.reefci.com
(haven’t stayed there yet thanks to Hurricane Ernesto in August 2012)
Rental apartments in the heart of Placencia: http://www.oneworldplacencia.com
Secluded resort on N. Ambergris Caye with snorkeling from shore: http://www.tranquilitybayresort.com