You can renovate an old home within a budget by freezing the design, getting multiple quotes and avoiding change orders.

Old home renovation may be trickier than building a new home because you may have to keep the existing structure and get rid of old materials like asbestos flooring etc. You need to be careful. 

Freeze the design: Communicate with your architect or designer in a way that all of your design requirements are incorporated in the plans. Try not to leave anything fluid or indecisive as it may affect your quote. Ask your architect if you could use any existing materials to save cost in the old home renovation. 

Get multiple quotes: Once the design is frozen, get a complete set of construction drawings from your architect and get multiple quotes from contractors. Usually 3-4 quotes are sufficient but you could get a few more. Do not make a final decision just based on the lowest cost, but evaluate construction quality and the contractors experience. Be sure to check references.

Avoid Change Orders: Most of the renovation projects go over the initial budget because too many changes are made to the design after construction has commenced. Changes made during the construction phase cost higher because you do not have the leverage to negotiate with the contractor which you had in the bidding phase. Keep the changes to the minimum and be sure to verify the contractors markup percentage in the change order. 

Check if you can use existing materials in the home renovation. Some materials may have harmful products and be sure to discard them according to the rules and regulations. Wood may be reused if it is structurally sound but certain tiles may not be. 

Some ideas to renovate and an old home on a budget are as follows:

Replace the front door

Wash the exterior

Paint Windows and shutters

Replace carpets and old flooring

Get new Appliances 

Replace your furnace and clean ducts

Check your roofing

Get your driveway paved

Replace old hardware