Most 2 bedrooms on Ambergris are in the 195-295 range I dont know of any budget condos but there are however lots of hotels that willfit your range for a room Lilys is VERY budget but popular Hotel Del rio would not be my first choice, probably paradise resort would be the one I pick however it is old and need refurbishing.
Realistically for a nice room your looking at $60 a night plus tax so for 2 rooms your looking at $120-125 a night which is doable.
Do you want to be in town or are you open to being out of town ???? also when are you planning on coming ??? this can also affect the price.
other places to look at should be
Banana Beach Resort (they have $60 rooms and its very nice)
Sunbreeze (depending on time you are coming)
Hell check with me if I have availability I can hook you up as a Scubaboard member (i am out of town though and like it that way plus I am not considered a budget hotel but I will work with you.
Also rubies is one of the most popular budget hotels on the island and they are on the beach but books very quickly.
check out
www.AmbergrisCaye.com and click on the lodging section which has hotels broken down into luxury mid priced and budget.
If you need any thing else dont hesitate to ask
Dive Safe
Gaz Cooper